bug: FoyerLayer ignores read args while filling full-object cache

[Xuanwo]

Describe the bug

FoyerLayer can ignore OpRead / OpStat arguments while filling the full-object cache.

In core/layers/foyer/src/full.rs, FullReader::fallback_open and fallback_read correctly call the inner accessor with self.args.clone(). However, read_full_object() fills the cache by calling:

• stat(&path_clone, OpStat::default())
• read(&path_clone, OpRead::default())

The cache key only includes path and version, derived from self.args.version().

This can make the cache-fill path observe different read conditions than the original reader request.

Steps to Reproduce

1. Enable FoyerLayer.
2. Read an object through reader_with(path) or read_with(path) with read arguments such as version, if_match, if_none_match, or other conditional read options.
3. Trigger a full-object cache miss so read_full_object() fills the cache.
4. Observe that the cache-fill path uses default read/stat args instead of the original request args.

Relevant code:

• fallback_open uses self.args.clone(): core/layers/foyer/src/full.rs
• fallback_read uses self.args.clone(): core/layers/foyer/src/full.rs
• cache-fill uses OpStat::default() and OpRead::default(): core/layers/foyer/src/full.rs
• cache key only includes path and version: core/layers/foyer/src/full.rs

Expected Behavior

The cache-fill path should preserve the semantics of the original read request.

At minimum:

• stat / read used for cache fill should be derived from self.args.
• Versioned reads should not accidentally fetch latest content and store it under a versioned cache key.
• Conditional reads such as if_match / if_none_match should either be respected during cache fill or explicitly bypass the cache after validating the condition.

Additional Context

This was found during post-merge review of the read-reader refactor. The new design makes Access::read return a reusable raw reader, so layers need to preserve OpRead semantics across both reader creation and later reader-side IO.

Suggested tests:

• FoyerLayer + reader_with(path).version(v) cache miss/hit behavior.
• FoyerLayer + read_with(path).if_match(...) cache miss/hit behavior.
• Ensure fallback and cache-fill paths observe the same read arguments.

Are you willing to submit a PR to fix this bug?

• Yes, I would like to submit a PR.