Update copilot-instructions.md (#1550)

### What

Remove unused deps from Copilot instructions: rust-src, cargo-watch,
cargo-nextest.

### Why

They aren't required tools.

Telling Copilot to use rust-src is likely to send it on tangents we
don't want it to take. Recompiling rust-src and relying on features that
Rust provides only through rust-src would harm the developer experience
of folks using the soroban-sdk, requiring them to also use rust-src
which is a not a common Rust developer experience.

cargo-watch is a deprecated tool and not recommended to use. Unclear to
me why Copilot would benefit from it since it is more likely to benefit
from choosing to run appropriate test commands after each change, which
the instructions already detail.

cargo-nextest is not needed. It may speed up test runs, but we don't use
it in the Makefile and Copilot will benefit from using the test targets
in the Makefile to ensure that the test vectors build before tests.

Author: leighmcculloch

.github/copilot-instructions.md

@@ -11,15 +11,11 @@ Always reference these instructions first and fallback to search or bash command
   - `curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh`
   - `rustup install stable`
   - `rustup +stable target add wasm32v1-none`
-  - `rustup +stable component add rust-src`
 - Install Rust nightly (required for documentation):
   - `rustup install nightly`
   - `rustup +nightly target add wasm32v1-none`
-  - `rustup +nightly component add rust-src`
 - Install required cargo tools:
   - `cargo install --locked cargo-hack`
-  - `cargo install --locked cargo-nextest`
-  - `cargo install --locked cargo-watch`
 
 ### Build Commands
 - **CRITICAL**: Format code first: `make fmt` -- takes ~1 second
@@ -54,7 +50,7 @@ After making changes to the SDK, always validate with these scenarios:
    - Use `log!` macro for debugging in tests
 
 3. **Contract Compilation Validation**:
-   - Build all test contracts: `make build` or `cargo hack build --target wasm32v1-none --release --workspace --exclude soroban-spec --exclude soroban-spec-rust --exclude soroban-ledger-snapshot`
+   - Build all test contracts: `make build`
    - Verify all Wasm files are generated correctly
    - Check that Wasm file sizes are reasonable (200B-3KB range)
    - Ensure no compilation warnings for the main SDK packages
@@ -111,8 +107,6 @@ After making changes to the SDK, always validate with these scenarios:
 
 ### Cargo Tools Usage
 - `cargo-hack` - Feature powerset testing and multi-target builds
-- `cargo-nextest` - Fast test execution (alternative to `cargo test`)
-- `cargo-watch` - File watching for development
 
 ### Build Artifacts
 - Wasm contracts output to `target/wasm32v1-none/release/*.wasm`
@@ -173,4 +167,4 @@ After creating a contract:
 1. Build Wasm: `cargo build --target wasm32v1-none --release`
 2. Test: `cargo test` (tests run on native target with std)
 3. Verify Wasm output in `target/wasm32v1-none/release/` (typically 500B-3KB)
-4. Check contract functions work as expected in test environment
+4. Check contract functions work as expected in test environment

CONTRIBUTING.md

@@ -14,26 +14,17 @@ Install rust stable:
 ```
 rustup install stable
 rustup +stable target add wasm32v1-none
-rustup +stable component add rust-src
 ```
 
 Install rust nightly:
 ```
 rustup install nightly
 rustup +nightly target add wasm32v1-none
-rustup +nightly component add rust-src
 ```
 
 Install cargo tools:
 ```
 cargo install --locked cargo-hack
-cargo install --locked cargo-nextest
-cargo install --locked cargo-watch
-```
-
-Install binaryen (for `wasm-opt`):
-```
-brew install binaryen
 ```
 
 ## Command Cheatsheet