Own the autoload map through ComposerAutoloadMapReader

[Firehed]

Summary

One service now owns reading the Composer autoload map.
ComposerAutoloadMapReader reads the map on first use and re-reads it when any file under vendor/composer/ changes — the one invalidatable for that path.
Both disk backends (AutoloadFilesBackend and ComposerMapBackend) hold the reader instead of a map snapshot and rebuild their derived indexes when the map instance changes.

Previously, the map was read once at boot into a value passed by construction to both backends, and a composer install that regenerated the autoload files could not reach either backend's derived state.
Now a regeneration reaches lookup, enumeration and search on the next query.

The invalidation composite routes vendor/composer/ paths through a wholesale flush of the maps cache decorator, since its per-path accounting cannot describe the blast radius of a whole-map change.

Test plan

• composer test (phpstan, deptrac, phpunit, phpcs) green
• New unit tests for ComposerAutoloadMapReader cover current/invalidate/fromMap and the vendor/composer prefix match
• New integration test covers the end-to-end flow: a regenerated autoload_psr4.php and autoload_files.php each reach both lookup and enumeration on the next query

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.65%. Comparing base (259ce1a) to head (36b3e4f).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #641   +/-   ##
=========================================
  Coverage     99.65%   99.65%           
- Complexity     1901     1913   +12     
=========================================
  Files           133      134    +1     
  Lines          4905     4940   +35     
=========================================
+ Hits           4888     4923   +35     
  Misses           17       17           

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