fix(fileio): satisfy decompression ABI lint

Use the pointer-width bit count for the decompression callback projection
assertion so the Rust archive remains clean under warnings-as-errors Clippy.
The assertion keeps the same byte offset on supported targets.

Test Plan:
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo fmt --manifest-path rust/Cargo.toml --all -- --check
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings

rust/src/fileio_asyncio.rs

@@ -631,7 +631,7 @@ const _: () = {
     );
     assert!(
         std::mem::offset_of!(FIO_rust_decompress_file_projection_t, decompress)
-            == FIO_RUST_DECOMPRESS_FILE_CALLBACK_OFFSET + 8 * size_of::<usize>()
+            == FIO_RUST_DECOMPRESS_FILE_CALLBACK_OFFSET + usize::BITS as usize
     );
     assert!(
         std::mem::offset_of!(FIO_rust_decompress_file_projection_t, clear_handler)