fix: increase MSRV to 1.71.1

The minimum supported Rust version is increased to 1.71.1 due to
positioned-io v0.3.4.

Also fix all Clippy warnings.

With a Rust version >= 1.68 it's possible to make crates.io checkouts
way faster on CI. Enable that option.

Author: vmx

.github/workflows/ci.yml

@@ -12,8 +12,7 @@ env:
   CARGO_INCREMENTAL: 0
   RUST_BACKTRACE: 1
   # Faster crates.io index checkout.
-  # Enable once the MSRV is >= 1.68
-  #CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
+  CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
   RUST_LOG: debug
 
 jobs:

rust-toolchain

@@ -1 +1 @@
-1.66.1
+1.71.1

src/hash_impl.rs

@@ -43,7 +43,7 @@ impl<H: Hasher, const N: usize> Hashable<H> for [u8; N] {
 
     #[allow(trivial_casts, unsafe_code)]
     fn hash_slice(data: &[[u8; N]], state: &mut H) {
-        let newlen = data.len() * mem::size_of::<[u8; N]>();
+        let newlen = mem::size_of_val(data);
         let ptr = data.as_ptr() as *const u8;
         state.write(unsafe { slice::from_raw_parts(ptr, newlen) })
     }

src/merkle.rs

@@ -1629,7 +1629,7 @@ impl<
 
         let mut data = S::new(size).expect("failed to create data store");
 
-        populate_data_par::<E, A, S, BaseTreeArity, _>(&mut data, iter)?;
+        populate_data_par::<E, A, S, _>(&mut data, iter)?;
         let root = S::build::<A, BaseTreeArity>(&mut data, leafs, row_count, None)?;
 
         Ok(MerkleTree {
@@ -1689,7 +1689,7 @@ impl<
             });
         }
 
-        populate_data_par::<E, A, S, BaseTreeArity, _>(&mut data, iter)?;
+        populate_data_par::<E, A, S, _>(&mut data, iter)?;
         let root = S::build::<A, BaseTreeArity>(&mut data, leafs, row_count, Some(config))?;
 
         Ok(MerkleTree {
@@ -2049,12 +2049,11 @@ pub fn populate_data<
     Ok(())
 }
 
-fn populate_data_par<E, A, S, BaseTreeArity, I>(data: &mut S, iter: I) -> Result<()>
+fn populate_data_par<E, A, S, I>(data: &mut S, iter: I) -> Result<()>
 where
     E: Element,
     A: Algorithm<E>,
     S: Store<E>,
-    BaseTreeArity: Unsigned,
     I: ParallelIterator<Item = E> + IndexedParallelIterator,
 {
     if !data.is_empty() {