Add JsonRpc outbound request timeout

[AArnott]

Why

Issue #1443 asks for a connection-wide way to bound outbound RPC calls instead of requiring each call site to create and dispose a linked CancellationTokenSource manually.

Fixes #1443

What changed

• Added JsonRpc.OutboundRequestTimeout as a nullable, disabled-by-default setting for response-expected outbound calls.
• Applied the timeout in the shared outbound invoke path so direct Invoke* APIs and proxy-generated calls behave the same way.
• Timeout-origin failures now throw TimeoutException and include nameof(JsonRpc.OutboundRequestTimeout) in the message so tests can assert on invariant text instead of localized English.
• When the caller's token is canceled, OperationCanceledException now escapes with the caller's original token rather than an internal linked token.
• Timeout-triggered cancellation still goes through the outbound cancellation strategy, so $/cancelRequest is sent even though the caller stops waiting immediately.
• Notifications remain unchanged.

Notes

The timeout only stops waiting on the client side. The server may still be processing the request, and the PR keeps that behavior explicit in the thrown timeout message.

Testing

• dotnet build -c Release
• Targeted timeout/cancellation tests on net9.0, net8.0, and net472
• Broader cancellation-focused regression sweep on net9.0 with TestCategory=FailsInCloudTest excluded

[Copilot]

Pull request overview

Adds a connection-wide outbound invocation timeout (JsonRpc.OutboundRequestTimeout) so both direct Invoke* APIs and proxy-generated calls can be bounded without per-call linked CancellationTokenSource management, with updated exception behavior and accompanying tests.

Changes:

• Introduces JsonRpc.OutboundRequestTimeout (nullable, disabled by default) with validation and documentation.
• Applies the timeout in the shared outbound invoke path and translates timeout-triggered cancellation to TimeoutException (with invariant message text containing nameof(JsonRpc.OutboundRequestTimeout)).
• Adds coverage for timeout behavior across direct invokes, proxies, notifications, and cancellation-strategy interactions.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/StreamJsonRpc.Tests/JsonRpcTests.cs	Adds direct invoke tests for outbound timeout behavior and precedence vs caller cancellation.
test/StreamJsonRpc.Tests/JsonRpcProxyGenerationTests.cs	Adds a proxy-call test verifying the JsonRpc-level outbound timeout is honored.
test/StreamJsonRpc.Tests/JsonRpcClient20InteropTests.cs	Adds a test ensuring notifications ignore outbound timeout.
test/StreamJsonRpc.Tests/CustomCancellationStrategyTests.cs	Adds a test verifying timeout-triggered cancellation still routes through cancellation strategy behavior.
src/StreamJsonRpc/Resources.resx	Adds resource strings for positive TimeSpan validation and timeout exception messaging.
src/StreamJsonRpc/JsonRpc.cs	Adds OutboundRequestTimeout and integrates timeout cancellation + exception shaping into outbound invoke pipeline.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.