remove several uses of unsafe (#8600)

This PR removes several uses of `unsafe`. I generally limited myself to
low hanging fruit that I could see. There are still a few remaining uses
of `unsafe` that looked a bit more difficult to remove (if possible at
all). But this gets rid of a good chunk of them.

I put each `unsafe` removal into its own commit with a justification for
why I did it. So I would encourage reviewing this PR commit-by-commit.
That way, we can legislate them independently. It's no problem to drop a
commit if we feel the `unsafe` should stay in that case.

crates/ruff_source_file/src/newlines.rs

@@ -58,11 +58,7 @@ impl<'a> UniversalNewlineIterator<'a> {
 pub fn find_newline(text: &str) -> Option<(usize, LineEnding)> {
     let bytes = text.as_bytes();
     if let Some(position) = memchr2(b'\n', b'\r', bytes) {
-        // SAFETY: memchr guarantees to return valid positions
-        #[allow(unsafe_code)]
-        let newline_character = unsafe { *bytes.get_unchecked(position) };
-
-        let line_ending = match newline_character {
+        let line_ending = match bytes[position] {
             // Explicit branch for `\n` as this is the most likely path
             b'\n' => LineEnding::Lf,
             // '\r\n'