refactor: extract config cache into a dedicated module with clear/reset support

[margaretjgu]

Closes #210

Summary

src/cli.ts used a bare module-level let earlyConfig to cache the early config load result and share it with the preAction hook. This works fine today since cli.ts is a top-level entry point, but if the same caching pattern were used in a library module there would be no way for tests to reset the cached state between runs — stale values could leak across test cases.

This PR extracts the cache into src/config/cache.ts with a clear public API:

• getCachedConfig() — returns the cached LoadConfigResult or undefined
• setCachedConfig(result) — stores a result in the cache
• clearCachedConfig() — resets the cache; intended for test cleanup

cli.ts is updated to call these instead of reading/writing the bare variable directly. Runtime behaviour is unchanged.

Changes

• src/config/cache.ts (new) — dedicated cache module
• src/cli.ts — replace bare let earlyConfig with getCachedConfig / setCachedConfig calls
• test/config/cache.test.ts (new) — 7 unit tests covering all three exports (100 % line/branch/function coverage)

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ COPYPASTE	jscpd	yes		no	no	8.26s
✅ REPOSITORY	gitleaks	yes		no	no	54.45s
✅ REPOSITORY	git_diff	yes		no	no	0.64s
✅ REPOSITORY	secretlint	yes		no	no	30.99s
✅ REPOSITORY	trivy	yes		no	no	16.65s
✅ TYPESCRIPT	eslint	6		0	0	4.88s

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[JoshMock]

A simpler implementation might be to update loadConfig to take an optional cached option, which is true by default (or a refresh option that's false by default). That way, config/loader.ts can handle its own caching internally and any place that needs to ensure it gets a fresh config every time doesn't have to import a separate module.

[margaretjgu]

Good suggestion, done. Deleted cache.ts and moved everything into loadConfig itself:

• loadConfig() returns the cached result on repeat calls (default behavior)
• loadConfig({ refresh: true }) bypasses the cache and loads fresh, updating the cache for subsequent calls
• clearConfigCache() exported from loader.ts for test cleanup between cases

cli.ts no longer imports a separate cache module. The preAction hook passes refresh: true when any CLI flag overrides are present (--config-file, --use-context, --command-profile), and defaults to the cached path otherwise.

cache.test.ts is rewritten to test caching behavior through loadConfig directly using a real temp config file.