add JRPC::Transport::Test to use in tests

[senid231]

closes #10

[Copilot]

Pull request overview

Adds a new in-process transport double JRPC::Transport::Test to the library (not autoloaded), so user code that talks to a JSON-RPC server via SimpleClient/SharedClient can be unit-tested without standing up a real server. The new transport combines the use cases previously served by the spec-only TransportDouble (for SimpleClient) and FakeSharedTransport (for SharedClient), exposing a high-level handler API (on('method') { ... }) plus a low-level escape hatch (push_response / push_raise, strict: false) for malformed/orphan/id-mismatch scenarios. A Unix socketpair backs the transport so SharedClient's IO.select loop works correctly.

Changes:

• New lib/jrpc/transport/test.rb implementing the Transport::Base contract with handlers, recordings, raw scripting, and FD lifecycle (close keeps FDs alive; shutdown and a GC finalizer release them).
• New spec/transport/test_spec.rb exercising the transport with both SimpleClient and SharedClient, including strict-mode, error mapping, fail_connect, and notification recording.
• Documentation in README.md (new "Testing" section) and a CHANGELOG.md entry.

Reviewed changes

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

File	Description
lib/jrpc/transport/test.rb	New library transport double with handler API, raw escape hatch, socketpair-backed IO.select support, and shutdown/finalizer FD cleanup.
spec/transport/test_spec.rb	New spec covering the transport against SimpleClient and SharedClient.
README.md	New "Testing" section documenting JRPC::Transport::Test, handlers, strict mode, raw API, and shutdown.
CHANGELOG.md	Changelog entry under "New" for the test transport.

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[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
jrpc	93%	81%	0	✔
Summary	93% (772 / 834)	81% (234 / 290)	0	✔