Bump mimalloc v2 (2.2.7) and v3 (3.2.8) submodules

[eduDorus]

This pull request updates the mimalloc submodules to newer commit versions. These changes ensure that our project uses the latest upstream improvements and bug fixes from the mimalloc memory allocator library.

Dependency updates:

• Updated the mimalloc v2 submodule in libmimalloc-sys/c_src/mimalloc/v2 to commit 6a53d72d46a1a641d8e5793db37cb2da60e04192.
• Updated the mimalloc v3 submodule in libmimalloc-sys/c_src/mimalloc/v3 to commit 7b7fca4b7013d77e356d96e055fec309cb3cbbd6.
  This pull request updates the mimalloc Rust bindings and its sys crate to newer versions, modernizes the codebase to use the latest Rust edition, and improves safety by consistently marking FFI calls as unsafe. It also updates the mimalloc C submodules to newer commits.

Dependency and edition updates:

• Bumped the mimalloc crate version to 0.1.49 and the libmimalloc-sys crate version to 0.1.45 in their respective Cargo.toml files. Both crates now use Rust edition 2024 for improved language features and compatibility. [1] [2]

Upstream mimalloc C library updates:

• Updated the mimalloc C submodules in libmimalloc-sys/c_src/mimalloc/v2 and libmimalloc-sys/c_src/mimalloc/v3 to newer commits, pulling in upstream improvements and bug fixes. [1] [2]

FFI and safety improvements:

• Marked all FFI function declarations as unsafe extern "C" in libmimalloc-sys/src/lib.rs to explicitly signal the need for unsafe usage.
• Ensured all calls to FFI functions in the GlobalAlloc implementation for MiMalloc are wrapped in unsafe blocks for better safety and clarity.