refactor(whatsrust): extract read synchronization wrappers

[Andiveli]

Summary

• Move mark_as_read and sync_chat_read into read_sync.rs.
• Preserve the public API, FFI ownership, error mapping, and asynchronous behavior.

Changes

• Added the crate-private read_sync module with explicit public facade reexports.
• Moved the borrowed CString regression test with its owning implementation.
• Kept the existing event-test visibility wiring compiling after the prior extraction chain.

Chain Context

• Start: PR refactor(whatsrust): extract action wrappers #315 (refactor/whatsrust-action-wrappers).
• End: read synchronization wrappers isolated.
• Dependency: immediate parent is PR refactor(whatsrust): extract action wrappers #315; no merge or CI wait requested.
• Diagram: #315 -> 📍 this PR -> message payloads -> send wrappers -> queries -> facade cleanup.
• Next: message_send.rs part A (payload ownership/builders and quote conversion).

Testing

• CARGO_TARGET_DIR=/home/samael/Escritorio/Programacion/public/wptui-public/target cargo check --workspace --all-targets
• CARGO_TARGET_DIR=/home/samael/Escritorio/Programacion/public/wptui-public/target cargo test -p whatsrust borrowed_ffi_arguments_can_be_reused_without_owned_pointer_leaks -- --test-threads=1
• CARGO_TARGET_DIR=/home/samael/Escritorio/Programacion/public/wptui-public/target cargo test --test whatsrust_api_contract -- --test-threads=1
• cargo fmt --all -- --check
• git diff --check
• Manual runtime testing: not applicable; this is a behavior-preserving FFI extraction.

Review Budget and Rollback

• Authored diff: 277 lines (150 additions + 127 deletions), within the 400-line limit.
• Rollback: revert a65bb20; removes read_sync.rs and restores the wrapper block without changing bridge behavior.

Out of scope

• No ABI, threading, error-policy, cache, leak, or panic behavior changes.
• No merge or CI wait.

Closes #316