`iter()` iterates over both keys and values, while `values()` iterates over just values. Also add `_mut()` versions. These replace the otherwise common idiom of iterating with `keys()` and using indexing to get the values, allowing for simpler code.
`iter()` iterates over both keys and values, while `values()` iterates over just values. Also add `_mut()` versions. These replace the otherwise common idiom of iterating with `keys()` and using indexing to get the values, allowing for simpler code.