Refactor append_file to avoid holding global mutex during I/O operations

[coderabbitai]

Problem

The append_file method in src/interpreter/mod.rs currently holds the global file_handles mutex while performing async I/O operations (seek/write/flush/sync). This blocks all other file operations unnecessarily during the I/O.

Current Implementation

The method performs all I/O operations while holding the lock:

let (_, file) = match file_handles.get_mut(handle_id) {
    Some(entry) => entry,
    None => return Err(format\!("Invalid file handle: {handle_id}")),
};

match AsyncSeekExt::seek(file, std::io::SeekFrom::End(0)).await {
    // ... all I/O operations while holding the lock
}

Proposed Solution

Clone the file handle while holding the lock, then drop the lock before performing I/O:

1. Get mutable reference to file and clone it while lock is held
2. Drop the lock immediately after cloning
3. Perform all async I/O operations on the cloned handle

This pattern should also be applied to other methods like write_file and close_file that have similar issues.

References

• PR: Enhances project version synchronization processes #165
• Comment: Enhances project version synchronization processes #165 (comment)

Files to Modify

• src/interpreter/mod.rs - append_file, write_file, close_file methods