test(bridge): add unit tests for should_retrigger() and retry exhaustion path

[bug-ops]

Description

PR #160 added should_retrigger() (client.rs) and the retry loop for ServerCancelled (-32802), but no unit tests cover this logic.

Missing coverage

• should_retrigger(None) → true (retrigger when data absent)
• should_retrigger({"retriggerRequest": false}) → false
• should_retrigger({"retriggerRequest": true}) → true
• Retry exhaustion: after 3 retries, the original ServerCancelled error is returned

Expected behavior

Unit tests in lsp/client.rs or a dedicated test module covering all four cases above.

Environment

• Introduced in PR fix(bridge): retry ServerCancelled requests and fix integration test readiness gate #160 (fix for integration tests: 5 tests fail in isolation with RA ServerCancelled/-32801 after readiness gate #127, bridge: LSP ServerCancelled (-32802) with retriggerRequest not retried — propagated as error to caller #128)