[SPARK-59435][UDF] Qualify UDF worker proto import paths

### What changes were proposed in this pull request?

This PR relocates the UDF worker protobuf definitions beneath
`udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/` and updates
their intra-proto imports to use the corresponding qualified paths.

This follows the namespaced source layouts used by other Spark protobuf
definitions, including:

- [Spark Connect common.proto](https://github.com/apache/spark/blob/master/sql/connect/common/src/main/protobuf/spark/connect/common.proto)
- [configuration schema](https://github.com/apache/spark/blob/master/common/config/src/main/protobuf/org/apache/spark/config/config_schema.proto)
- [status store types](https://github.com/apache/spark/blob/master/core/src/main/protobuf/org/apache/spark/status/protobuf/store_types.proto)
- [streaming state message](https://github.com/apache/spark/blob/master/sql/core/src/main/protobuf/org/apache/spark/sql/execution/streaming/StateMessage.proto)

### Why are the changes needed?

The UDF worker definitions previously used generic bare import names such as
`common.proto` and `udf_message.proto`. Relocating them establishes stable,
qualified import paths, avoiding ambiguity if Spark protobuf sources are later
collected, indexed, or compiled alongside definitions with similarly named
files.

The message definitions, generated Java package, and wire format are unchanged.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

- `protoc` compilation of the relocated UDF worker protobuf definitions.
- `build/mvn -pl udf/worker/proto,udf/worker/grpc -am -DskipTests compile`
- `build/mvn -pl udf/worker/grpc -am test`
  - UDF worker core: 59 tests passed.
  - UDF worker gRPC: 60 tests passed.

### Was this patch authored or co-authored using generative AI tooling?

Yes.

Closes #58738 from haiyangsun-db/SPARK-59435-qualify-udf-worker-proto-imports.

Authored-by: Haiyang Sun <haiyang.sun@databricks.com>
Signed-off-by: Hyukjin Kwon <hyukjin.kwon@databricks.com>
(cherry picked from commit f3b1883)
Signed-off-by: Hyukjin Kwon <hyukjin.kwon@databricks.com>

Author: haiyangsun-db

udf/worker/README.md

@@ -34,10 +34,11 @@ provisioning service or daemon).
 ```
 udf/worker/
 ├── proto/                        -- protobuf message classes only (protobuf-java)
-│     worker_spec.proto           -- UDFWorkerSpecification protobuf
-│     udf_message.proto           -- UDF execution protocol messages (Init, UdfPayload, ...)
-│     udf_service.proto           -- UdfWorker gRPC service (Execute, Manage)
-│     common.proto                -- shared enums (UDFWorkerDataFormat, etc.)
+│   └── src/main/protobuf/org/apache/spark/udf/worker/
+│       worker_spec.proto         -- UDFWorkerSpecification protobuf
+│       udf_message.proto         -- UDF execution protocol messages (Init, UdfPayload, ...)
+│       udf_service.proto         -- UdfWorker gRPC service (Execute, Manage)
+│       common.proto              -- shared enums (UDFWorkerDataFormat, etc.)
 │
 ├── core/                         -- abstract interfaces
 │     WorkerDispatcher.scala      -- creates sessions, manages worker lifecycle
@@ -56,7 +57,7 @@ udf/worker/
       GrpcWorkerChannel.scala     -- owns a Netty gRPC channel and event loop
       GrpcWorkerSession.scala     -- one UDF execution over an Execute stream
       UnixDomainSocketTransport.scala -- selects native epoll/kqueue transport
-      (generated)                 -- UdfWorkerGrpc stubs from proto/udf_service.proto
+      (generated)                 -- UdfWorkerGrpc stubs from the UDF worker service proto
 ```
 
 The `core/` package defines abstract interfaces that are independent of how
@@ -67,7 +68,7 @@ obtaining workers from a provisioning service or daemon.
 
 The `grpc/` module owns the concrete direct dispatcher, channel and session
 implementations, native Unix-domain-socket transport selection, gRPC service-stub
-generation (from `proto/`'s `udf_service.proto`), and the gRPC runtime dependencies.
+generation (from the UDF worker service proto above), and the gRPC runtime dependencies.
 Keeping gRPC here means `proto/`, `core/`, and their consumers (`core`, `catalyst`,
 `sql/core`) carry no gRPC dependency on their classpath.
 
@@ -81,9 +82,10 @@ Engine -> Worker:  Init -> PayloadChunk* -> (DataRequest)* -> Finish (Cancel)?
 Worker -> Engine:          InitResponse  -> (DataResponse)* -> (ErrorResponse)? -> (FinishResponse | CancelResponse)
 ```
 
-See `udf/worker/proto/src/main/protobuf/udf_message.proto` for the complete
-message definitions, ordering invariants, and error contract, and
-`udf_service.proto` for the gRPC service.
+See `udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/udf_message.proto`
+for the complete message definitions, ordering invariants, and error contract, and
+`udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/udf_service.proto`
+for the gRPC service.
 
 ### Direct worker creation
 

…ker/proto/src/main/protobuf/common.proto …org/apache/spark/udf/worker/common.protoudf/worker/proto/src/main/protobuf/common.proto renamed to udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/common.proto udf/worker/proto/src/main/protobuf/common.proto renamed to udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/common.proto

@@ -17,7 +17,7 @@
 
 syntax = "proto3";
 
-import "common.proto";
+import "org/apache/spark/udf/worker/common.proto";
 
 package org.apache.spark.udf.worker;
 

…roto/src/main/protobuf/udf_message.proto …pache/spark/udf/worker/udf_message.protoudf/worker/proto/src/main/protobuf/udf_message.proto renamed to udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/udf_message.proto udf/worker/proto/src/main/protobuf/udf_message.proto renamed to udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/udf_message.proto

@@ -17,7 +17,7 @@
 
 syntax = "proto3";
 
-import "udf_message.proto";
+import "org/apache/spark/udf/worker/udf_message.proto";
 
 package org.apache.spark.udf.worker;
 

…roto/src/main/protobuf/udf_service.proto …pache/spark/udf/worker/udf_service.protoudf/worker/proto/src/main/protobuf/udf_service.proto renamed to udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/udf_service.proto udf/worker/proto/src/main/protobuf/udf_service.proto renamed to udf/worker/proto/src/main/protobuf/org/apache/spark/udf/worker/udf_service.proto

@@ -17,7 +17,7 @@
 
 syntax = "proto3";
 
-import "common.proto";
+import "org/apache/spark/udf/worker/common.proto";
 
 package org.apache.spark.udf.worker;