feat: Add RSpec test adapter and perform project cleanup (Jules test)

[kbwo]

This commit introduces a new test adapter for the RSpec testing framework and includes general code cleanup.

RSpec Adapter Features:

• Implements the Runner trait for RSpec.
• Uses tree-sitter-ruby for test discovery from *_spec.rb files, identifying describe, context, and it blocks.
• Executes RSpec tests using the rspec -f json command and parses the JSON output to generate diagnostics for failed tests.
• Detects RSpec workspaces by looking for Gemfile or .rspec files.
• Includes a demo RSpec project (demo/rspec_project) for testing.
• Adds integration tests (crates/adapter/tests/rspec_test.rs) covering workspace detection, test discovery, and diagnostic parsing.

Cleanup and Fixes:

• I refactored the RSpec adapter to be fully synchronous, resolving previous compilation issues with the Runner trait.
• I removed unused imports and dead code in the RSpec adapter files.
• I ensured the crates/adapter/src/runner/phpunit.rs uses the correct tree-sitter PHP language function, confirming a previous fix.
• I verified that the entire project builds successfully using cargo build --all-targets.
• I confirmed all RSpec-specific tests pass. Pre-existing test failures in Jest, Node, and Vitest adapters remain and are noted as out of scope for this change.

The implementation adheres to the synchronous nature of the Runner trait, ensuring correct integration with the existing adapter framework.