Add caching support to Wayfinder route generation

[rohan2388]

Summary

Introduces a basic caching mechanism to prevent unnecessary regeneration of route/action files when nothing has changed.
This avoids deleting and rewriting hundreds of files (500+) on each run which can cause VS Code to lag or crash on Linux systems and significantly improves performance.

Changes

src/Route.php:

Added controllerAbsolutePath(), cacheKey(), and cacheValue() for unique cache keys and content hashes.

src/GenerateCommand.php:

Added $cached and $generatedFiles arrays to track file generation.
Writes two new cache files:
cache.json — stores route-level cache data.
generated_files.json — tracks all generated files.