feat(driver): buffer pool allocator

[George-Miao]

Closes #472

cc @inklesspen1rus

Added buffer pool trait and default implementation, moved platform-agnostic part of the buffer pool into root level of driver, and added some tests.

Maybe in future we can also add an mmap implementation based on the test, and use VirtualAlloc on windows, what do you think @Berrysoft?

[Copilot]

Pull request overview

This PR introduces a pluggable buffer-pool allocation mechanism in compio-driver to address performance/alignment issues observed with different global allocators and O_DIRECT (Issue #472). It extracts buffer-pool logic into a dedicated module, adds a BufferAllocator trait with a default implementation, and wires allocator selection through ProactorBuilder.

Changes:

• Added BufferAllocator + default BoxAllocator, and refactored buffer-pool implementation into compio-driver/src/buffer_pool.rs.
• Extended ProactorBuilder/Proactor initialization to carry a buffer allocator selection (buffer_pool_allocator).
• Added Unix integration tests using an mmap-based allocator; updated sys modules to expose BufControl internally and adjusted imports/visibility.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
compio-driver/src/buffer_pool.rs	New buffer-pool module, allocator trait/default, and pool/ref implementation.
compio-driver/src/lib.rs	Builder + proactor changes to store/configure the buffer pool allocator and re-export API.
compio-driver/src/sys/mod.rs	Adjusted sys module exports to align with moved buffer-pool code.
compio-driver/src/sys/buffer_pool.rs	Refactored sys-side buffer control wrapper and fallback module visibility.
compio-driver/src/sys/iour/buffer_pool.rs	Updated imports/visibility for BufControl to match new module layout.
compio-driver/src/sys/fusion/mod.rs	Adjusted BufControl re-export visibility.
compio-driver/src/sys/fusion/buffer_pool.rs	Updated imports/visibility for fusion BufControl.
compio-driver/tests/buffer_pool.rs	Added integration tests for buffer pool behavior and an mmap allocator.
compio-driver/Cargo.toml	Added nix dev-dependency for mman and configured the new test target.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.