chore: remove unnecessary cast usize

lint message: casting to the same type is unnecessary (`u64` -> `u64`)
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#unnecessary_cast

+ disable `clippy::unnecessary_cast` for update_disk_usage
where the size of the input values depends on the platform

src/rpc/system.rs

@@ -856,6 +856,7 @@ impl NodeStatus {
 		};
 
 		let mount_avail = |path: &Path| match statvfs(path) {
+			#[allow(clippy::unnecessary_cast)]
 			Ok(x) => {
 				let avail = x.blocks_available() as u64 * x.fragment_size() as u64;
 				let total = x.blocks() as u64 * x.fragment_size() as u64;