feat(logging): add minimum level to in-memory logger

[alexsmolya]

Summary

• InMemoryRuntimeLogger previously recorded every supported level with no configurable threshold.
• It now accepts optional level?: RuntimeLogLevel.
• The default remains debug, preserving existing all-level recording.
• Explicit thresholds share the existing priority semantics used by ConsoleRuntimeLogger.
• Filtering occurs before capacity eviction and append.
• InMemoryRuntimeLoggerOptions is publicly exported.

Validation

• Focused logger suite: 29/29 passed.
• Full npm run verify: 231/231 tests passed with coverage thresholds.
• Format, lint, typecheck, build, and git diff --check passed.

Fixes #266