refactor: Generate Linter -> RuleSelector mapping via macro
To enable ruff_dev to automatically generate the rule Markdown tables in
the README the ruff library contained the following function:
Linter::codes() -> Vec<RuleSelector>
which was slightly changed to `fn prefixes(&self) -> Prefixes` in
9dc66b5a6546926aff0d04a0280401f939f3a3d8 to enable ruff_dev to split
up the Markdown tables for linters that have multiple prefixes
(pycodestyle has E & W, Pylint has PLC, PLE, PLR & PLW).
The definition of this method was however largely redundant with the
#[prefix] macro attributes in the Linter enum, which are used to
derive the Linter::parse_code function, used by the --explain command.
This commit removes the redundant Linter::prefixes by introducing a
same-named method with a different signature to the RuleNamespace trait:
fn prefixes(&self) -> &'static [&'static str];
As well as implementing IntoIterator<Rule> for &Linter. We extend the
extisting RuleNamespace proc macro to automatically derive both
implementations from the Linter enum definition.
To support the previously mentioned Markdown table splitting we
introduce a very simple hand-written method to the Linter impl:
fn categories(&self) -> Option<&'static [LinterCategory]>;
