Inject a scalable buddy system allocator to OSTD

Co-authored-by: Zhe Tang <tangzh@stu.pku.edu.cn>

osdk/deps/frame-allocator/src/lib.rs

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+// SPDX-License-Identifier: MPL-2.0
+
+#![no_std]
+#![deny(unsafe_code)]
+
+//! An implementation of the global physical memory frame allocator for
+//! [OSTD](https://crates.io/crates/ostd) based kernels.
+//!
+//! # Background
+//!
+//! `OSTD` has provided a page allocator interface, namely [`GlobalFrameAllocator`]
+//! and [`global_frame_allocator`] procedure macro, allowing users to plug in
+//! their own frame allocator into the kernel safely. You can refer to the
+//! [`ostd::mm::frame::allocator`] module for detailed introduction.
+//!
+//! # Introduction
+//!
+//! This crate is an implementation of a scalable and efficient global frame
+//! allocator based on the buddy system. It is by default shipped with OSDK
+//! for users that don't have special requirements on the frame allocator.
+//!
+//! [`GlobalFrameAllocator`]: ostd::mm::GlobalFrameAllocator
+//! [`global_frame_allocator`]: ostd::global_frame_allocator
+
+mod allocator;
+mod chunk;
+mod set;
+
+#[cfg(ktest)]
+mod test;
+
+pub use allocator::{load_total_free_size, FrameAllocator};