Replace libz-rs-sys FFI wrapper with direct zlib-rs usage

[Copilot]

Eliminates FFI layer by using zlib-rs directly instead of its C-compatible wrapper libz-rs-sys. The underlying implementation is identical; this removes an unnecessary indirection layer.

Changes

Dependency update (gix-features/Cargo.toml):

• libz-rs-sys → zlib-rs

API migration (gix-features/src/zlib/):

• libz_rs_sys::inflateInit_() → zlib_rs::inflate::init()
• libz_rs_sys::inflate() → zlib_rs::inflate::inflate()
• libz_rs_sys::deflate() → zlib_rs::deflate::deflate()
• Similar changes for reset() and end() functions

Safety boundary:

• Minimal unsafe remains only for z_stream ↔ typed stream conversions
• Added Send/Sync impls and safety comments
• Compression/decompression logic now runs through pure Rust API

Example

// Before: FFI wrapper
unsafe {
    libz_rs_sys::inflateInit_(&mut stream, libz_rs_sys::zlibVersion(), size);
}
unsafe { libz_rs_sys::inflate(&mut stream, flush) }

// After: Direct Rust API
zlib_rs::inflate::init(&mut stream, config);
let stream = unsafe { zlib_rs::inflate::InflateStream::from_stream_mut(&mut stream) };
unsafe { zlib_rs::inflate::inflate(stream, flush) }  // Pure Rust internally

Note: deflate() is fully safe; inflate() remains unsafe in zlib-rs API due to output buffer handling.

Original prompt

Replace libz-rs-sys with zlib-rs, which is the underlying implementation. That way there is no unsafe code related to zlib usage.

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[Copilot]

Pull request overview

This PR modernizes the zlib integration by migrating from the FFI wrapper libz-rs-sys to the direct Rust API zlib-rs. The change eliminates unnecessary C FFI boundaries while maintaining identical underlying implementation. All unsafe operations related to zlib usage are removed, with the new API handling stream management through pure Rust types (zlib_rs::Deflate and zlib_rs::Inflate).

Key Changes:

• Dependency upgrade from libz-rs-sys 0.5.2 to zlib-rs 0.5.4
• Refactored compression/decompression APIs to use direct Rust methods instead of FFI calls
• Removed manual Drop, Send, and Sync implementations (now auto-derived from Rust types)
• Added new error variant NeedDict to handle dictionary-required scenarios in decompression

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 3 comments.

File	Description
gix-features/Cargo.toml	Updates dependency from libz-rs-sys to zlib-rs with version bump to 0.5.4
Cargo.lock	Reflects the dependency change and version update in the lock file
gix-features/src/zlib/stream/deflate/mod.rs	Migrates Compress from FFI-based z_stream to zlib_rs::Deflate; removes unsafe blocks and manual trait impls; adds DataError variant
gix-features/src/zlib/mod.rs	Migrates Decompress from FFI-based z_stream to zlib_rs::Inflate; removes unsafe blocks and manual trait impls; adds NeedDict error variant