[0.1.5] Limit concurrency: discard stale annotation results per file; add SDK env tests

[unurgunite]

Description

Two changes in this PR:

1. Concurrency: discard stale annotation results per file

When the IDE triggers multiple rapid annotations for the same file (e.g. during a series of quick saves), only the last check result is now applied. Each file has a generation counter (ConcurrentHashMap in DocscribeAnnotator.fileGeneration) — if a newer check starts while an older one is still running, the older result is discarded on completion.

Before: rapid saves triggered N concurrent bundle exec docscribe calls for the same file. All N results were applied in sequence, with the last one overwriting — wasted work and potential race conditions.

After: each file has a generation counter incremented at the start of doAnnotate(). On completion, the saved generation is compared to the current value. If they differ, the result is discarded. Only the latest check's annotations reach the editor.

2. Tests + KDoc for Ruby SDK environment

PR #32 added buildSdkEnvironment() and DefaultCommandExecutor(environment) but lacked tests and docs:

• DefaultCommandExecutor — KDoc for environment parameter (how SDK PATH injection works)
• DefaultCommandExecutor with environment does not throw — integration test verifying the env constructor works with runDocscribe()

Files

File	Change
DocscribeAnnotator.kt	Generation counter + discard logic + KDoc
DocscribeAnnotatorTest.kt	3 new tests: null-safe return, generation increments, per-file isolation
DocscribeRunner.kt	KDoc for DefaultCommandExecutor.environment
DocscribeRunnerTest.kt	Test for DefaultCommandExecutor(environment)
CHANGELOG.md	Entry for stale result discard

Checklist

• Tests pass (./gradlew test)
• Formatting clean (./gradlew spotlessCheck)
• Static analysis clean (./gradlew detekt)
• Plugin verified (./gradlew verifyPlugin)
• CHANGELOG updated