style: improve use of std api

- replace get(0) by first()
lint message: accessing first element with `objs.get(0)`
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#get_first
- use io::Error::other method available since Rust 1.87
lint message: this can be `std::io::Error::other(_)`
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#io_other_error
- implement From<_> instead of Into<_>
lint message: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
help: `impl From<Local> for Foreign` is allowed by the orphan rules, for more information see
            https://doc.rust-lang.org/reference/items/implementations.html#trait-implementation-coherence
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#from_over_into
- use next_back instead of rev + next
lint message: manual backwards iteration
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#manual_next_back
- use saturating_sub instead of manual implement it
lint message: manual arithmetic check found
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#implicit_saturating_sub
- add Default implementation for Checksummer
use derived Default ans use it in new, as new set all value to None
lint message: you should consider adding a `Default` implementation for `Checksummer`
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#new_without_default
- use `any` instead of `find` + `is_some`
lint message: called `is_some()` after searching an `Iterator` with `find`
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#search_is_some
- replace `and_then` + `Some(_)` with `map`
lint message: using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#bind_instead_of_map
- replace `skip_while` + `next` with `find`
lint message: called `skip_while(<p>).next()` on an `Iterator`
help: this is more succinctly expressed by calling `.find(!<p>)` instead
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#skip_while_next
- use `matches!` instead of manual implementation
lint message: match expression looks like `matches!` macro
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#match_like_matches_macro
- use `keys` and `values methods insteads of iterating and ignoring either the keys or values.
help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#iter_kv_map

src/api/common/signature/checksum.rs

@@ -63,6 +63,7 @@ pub struct ExpectedChecksums {
 	pub extra: Option<ChecksumValue>,
 }
 
+#[derive(Default)]
 pub struct Checksummer {
 	pub crc32: Option<CrcDigest>,
 	pub crc32c: Option<CrcDigest>,
@@ -84,14 +85,7 @@ pub struct Checksums {
 
 impl Checksummer {
 	pub fn new() -> Self {
-		Self {
-			crc32: None,
-			crc32c: None,
-			crc64nvme: None,
-			md5: None,
-			sha1: None,
-			sha256: None,
-		}
+		Default::default()
 	}
 
 	pub fn init(expected: &ExpectedChecksums, add_md5: bool) -> Self {