Protobuf

[platypii]

Add OTLP/HTTP protobuf support

• Accept Content-Type: application/x-protobuf on /v1/{traces,metrics,logs} alongside existing JSON, returning protobuf responses for protobuf requests
• Add zero-dependency protobuf wire-format codec (src/protobuf.js) — varint, fixed32/64, length-delimited, zigzag — no .proto files or generated code
• Add OTLP decoders for traces, metrics (all data point types: gauge/sum/histogram/exponential-histogram/summary), and logs, plus shared Resource/InstrumentationScope/AnyValue helpers under src/otlp/
• Decoded protobuf payloads flow through the same handler(signal, data) path as JSON, so Collector writes them to the same <signal>.jsonl files with no further changes
• Malformed protobuf → 400; unknown content types → 415 with updated error message
• Tests: test/protobuf.test.js (wire format), test/otlp.test.js (decoders, ~430 lines), plus server-level coverage for the protobuf path