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/db/fjall_adapter.rs

@@ -287,7 +287,7 @@ impl<'a> ITx for FjallTx<'a> {
 	}
 	fn len(&self, tree_idx: usize) -> TxOpResult<usize> {
 		let tree = self.get_tree(tree_idx)?;
-		Ok(self.tx.len(tree)? as usize)
+		Ok(self.tx.len(tree)?)
 	}
 
 	fn insert(&mut self, tree_idx: usize, key: &[u8], value: &[u8]) -> TxOpResult<()> {

src/net/recv.rs

@@ -89,7 +89,7 @@ pub(crate) trait RecvLoop: Sync + 'static {
 			let has_cont = (size & CHUNK_FLAG_HAS_CONTINUATION) != 0;
 			let is_error = (size & CHUNK_FLAG_ERROR) != 0;
 			let size = (size & CHUNK_LENGTH_MASK) as usize;
-			let mut next_slice = vec![0; size as usize];
+			let mut next_slice = vec![0; size];
 			read.read_exact(&mut next_slice[..]).await?;
 
 			let packet = if is_error {

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;