Error on zero tab width (#6429)

## Summary

Error if `tab-size` is set to zero (it is used as a divisor). Closes
#6423.

Also fixes a typo.

## Test Plan

Running ruff with a config

```toml
[tool.ruff]
tab-size = 0
```

returns an error message to the user saying that `tab-size` must be
greater than zero.

crates/ruff_cache/src/cache_key.rs

@@ -2,6 +2,7 @@ use std::borrow::Cow;
 use std::collections::hash_map::DefaultHasher;
 use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
 use std::hash::{Hash, Hasher};
+use std::num::NonZeroU8;
 use std::ops::{Deref, DerefMut};
 use std::path::{Path, PathBuf};
 
@@ -205,6 +206,13 @@ impl CacheKey for i8 {
     }
 }
 
+impl CacheKey for NonZeroU8 {
+    #[inline]
+    fn cache_key(&self, state: &mut CacheKeyHasher) {
+        state.write_u8(self.get());
+    }
+}
+
 macro_rules! impl_cache_key_tuple {
     () => (
         impl CacheKey for () {