feat(filesystem):add async vfs path

[Koichi98]

Description

This PR ports AsyncVfsPath for no_std environments. File systems that implement AsyncFileSystem, which was introduced in a previous PR, will be able to perform various file operations using this AsyncVfsPath.

This pull request primarily involves changes due to VfsError becoming VfsError(PR #548), switching from std::time::SystemTime to awkernel_lib::time::Time, and removing unnecessary comments.

std::io::Read read_to_string() is used in read_to_string() method of this AsyncVfsPath. Therefore, I've implemented it myself in this PR, since we didn't have read_to_string() method in our AsyncSeekAndRead trait. It seems like it contains two unnecessary copies, but this is to follow the rule below.

• String's invariant that it must always contain valid UTF-8. Rust does not permit this state to occur in safe code.

Related links

#548 (delete type parameter E from VfsError)
#539 (introducing AsyncFilesystem)
#511 (main PR)

How was this PR tested?

Notes for reviewers

As a result of these recent deletions, awkernel_lib/src/file/vfs/path.rs is now almost empty, containing only helper functions necessary for AsyncVfsPath and the definition of VfsMetadata. It's highly likely that this content will eventually be moved to awkernel_async_lib/src/file/path.rs, but I'm holding off on that for this PR to avoid making it overly complex.

[Copilot]

Pull Request Overview

This PR adapts the synchronous and asynchronous virtual filesystem paths for no_std environments, replacing SystemTime with a custom Time type and restructuring modules to separate sync (awkernel_lib) and async (awkernel_async_lib) code. Key changes include:

• Migrated awkernel_lib VFS path API to use alloc and Time and exposed PathLike publicly.
• Introduced an async VFS layer in awkernel_async_lib with updated file-system traits, AsyncVfsPath, and a new async_copy helper.
• Updated module exports (pub mod path/file) and added new dependencies (async-trait, async-recursion).

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
awkernel_lib/src/file/vfs/path.rs	Switched imports to alloc, replaced SystemTime with Time, made PathLike public
awkernel_lib/src/file/vfs.rs	Re-exported path module
awkernel_async_lib/src/lib.rs	Added top-level file module
awkernel_async_lib/src/file/path.rs	Rewrote async path logic, updated method signatures, added async_copy, removed many docs
awkernel_async_lib/src/file/filesystem.rs	Extended AsyncSeekAndRead with read_to_string, added Debug to AsyncFileSystem
awkernel_async_lib/src/file.rs	Introduced filesystem and path modules
awkernel_async_lib/Cargo.toml	Added async-trait and async-recursion dependencies

Comments suppressed due to low confidence (5)

awkernel_async_lib/src/file/path.rs:1

• [nitpick] Most public methods have lost their doc comments; adding concise documentation (including examples) for key APIs like join, read_dir, and copy_file will improve discoverability and maintainability.

//! Async virtual filesystem path

awkernel_async_lib/src/file/filesystem.rs:113

• Adding a Debug bound to AsyncFileSystem is a breaking change for existing implementations; consider documenting this change or making the bound optional to preserve backward compatibility.

pub trait AsyncFileSystem: Sync + Send + Debug {

awkernel_async_lib/src/file/path.rs:58

• [nitpick] Changing AsyncVfsPath::new from a generic parameter to a Box<dyn AsyncFileSystem> reduces API flexibility; consider providing a generic constructor or helper to allow callers to pass concrete types directly.

    pub fn new(filesystem: Box<dyn AsyncFileSystem + Send + Sync>) -> Self {

awkernel_async_lib/src/file/path.rs:613

• The new async_copy function does not have any accompanying tests; adding unit tests (including error paths) will help ensure correctness and prevent regressions.

pub async fn async_copy<R, W>(reader: &mut R, writer: &mut W) -> VfsResult<u64>

awkernel_lib/src/file/vfs/path.rs:11

• The Vec import does not appear to be used in this file after trimming its contents; consider removing it to avoid an unused import.

};