Allow injecting model catalog caches (#36992)

## What changed

- Add the public asynchronous `ModelsCache` contract and cache entry/error types.
- Let model providers and `OpenAiModelsManager` accept caller-provided cache implementations while retaining the existing file-backed cache by default.
- Treat cache read failures as misses, keep cache write failures non-fatal, and support refreshing an entry's TTL after ETag revalidation.
- Continue to prefer an explicitly configured static model catalog over an injected cache.

## Testing

- Cover injected cache hits, read and write failures, TTL refreshes, and end-to-end model selection.
- Verify that the file-backed implementation satisfies the new cache contract and does not serve expired entries before revalidation.

GitOrigin-RevId: eef957a317910b8502a0c20f8fc112f689d5e389

codex-rs/models-manager/src/lib.rs

@@ -1,4 +1,4 @@
-pub(crate) mod cache;
+pub mod cache;
 pub mod collaboration_mode_presets;
 pub(crate) mod config;
 pub mod manager;