[2.x] fix: resolve VersionerInterface from container; cache rev-manifest reads

[imorland]

Summary

RevisionCompiler, JsDirectoryCompiler, and Document declared a VersionerInterface property but instantiated FileVersioner directly in their constructors. The interface contract was unenforceable — $container->bind(VersionerInterface::class, MyVersioner::class) had no effect on these classes.

This PR:

1. Binds VersionerInterface in FrontendServiceProvider (defaulting to FileVersioner against the flarum-assets disk) and resolves it via the container in all three call sites. Local-disk installs are unchanged (same default binding); installs on remote storage can now bind a faster implementation and have it take effect everywhere.
2. Caches the parsed manifest in-memory on FileVersioner. With the binding now a singleton, all ~6 compilers + Document per request share one VersionerInterface instance — previously each read and JSON-decoded rev-manifest.json independently. On S3-backed installs this was ~12 round-trips per request just for asset URL resolution; now it's one.

Fixes #4637

Changes

• framework/core/src/Frontend/FrontendServiceProvider.php — bind VersionerInterface to a FileVersioner singleton scoped to the flarum-assets filesystem.
• framework/core/src/Frontend/Compiler/RevisionCompiler.php and JsDirectoryCompiler.php — drop the inline new FileVersioner(...), accept VersionerInterface via constructor (autowired). Both classes are @internal and resolved through the container by Frontend\Assets, so no caller needs updating.
• framework/core/src/Frontend/Document.php — replace the FilesystemFactory $filesystem constructor parameter with VersionerInterface $versioner. Resolved via $container->makeWith() from Frontend.php — autowiring picks up the new arg.
• framework/core/src/Frontend/Compiler/FileVersioner.php — per-instance manifest cache with write-through. putRevision() updates both disk and the cache; getRevision() and allRevisions() read from the cache. The CLI compile path constructs fresh containers, so per-instance lifetime is correct (no stale-manifest worries across processes).
• New framework/core/tests/unit/Frontend/Compiler/FileVersionerTest.php — 5 tests pinning down read-once-per-instance, missing keys, missing manifest, write-through cache update, and key removal via null revision.

Backward compatibility

• Document::__construct signature change is the only break. The sixth parameter FilesystemFactory $filesystem is now VersionerInterface $versioner. Subclasses that call parent::__construct(...) with positional arguments will need to update; named arguments are forward-compatible. Most extensions don't subclass Document and aren't affected. Worth a note in the 2.0 dev upgrade guide.
• RevisionCompiler and JsDirectoryCompiler are @internal and only resolved through the container; the new constructor parameter is autowired from the binding.

Test plan

• Unit tests: 5/5 pass (FileVersionerTest).
• Frontend integration tests: 10/10 pass (full document rendering exercises all three resolved instantiation paths).
• Admin integration tests: 2/2 pass.
• Manual: confirm forum/admin pages render normally on a local-disk install.
• Manual: confirm php flarum assets:publish and php flarum cache:clear still write a valid rev-manifest.json and bundles serve correctly.
• Manual on S3 install (if available): confirm filesystem call count for asset URL resolution drops from ~12 to 1 per request.

Related

• [2.x] srcsetFor() on AvatarUploader makes 3 remote exists() calls per user serialized — ~120ms+ per page on remote-disk installs #4635 — same shape (Flysystem exists() calls in a per-request hot path) on the avatar srcsetFor accessor; outside scope of this PR.