feat: add telemetry tracking for inline assist suggestion acceptance/rejection

[markijbema]

Summary

This PR adds telemetry tracking for inline assist (autocomplete) suggestions to measure acceptance and rejection rates.

Changes

• Added tracking for INLINE_ASSIST_ACCEPT_SUGGESTION event when users accept inline code suggestions
• Added tracking for INLINE_ASSIST_REJECT_SUGGESTION event when:
  • No suggestion is available (empty LLM response)
  • A suggestion times out after 10 seconds without being accepted
• Protected all telemetry calls with TelemetryService.hasInstance() checks for backward compatibility

Implementation Details

The implementation tracks user interactions with inline suggestions:

1. Acceptance: Registered a VSCode command that fires when suggestions are accepted
2. Rejection: Tracks both immediate rejection (no suggestion) and timeout-based rejection (10s)

Testing

• Added comprehensive test suite in GhostInlineCompletionProvider.telemetry.spec.ts
• All 4 new telemetry tests pass ✅
• All 63 existing tests continue to pass ✅
• Total: 111 tests passing

Impact

This telemetry will provide valuable metrics on:

• Suggestion acceptance rates
• User engagement with inline assist
• Quality of generated suggestions

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Latest commit: 9f0fb1d

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