## Summary
As the title says, this PR removes the `Message::to_rule` method by
replacing related uses of `Rule` with `NoqaCode` (or the rule's name in
the case of the cache). Where it seemed a `Rule` was really needed, we
convert back to the `Rule` by parsing either the rule name (with
`str::parse`) or the `NoqaCode` (with `Rule::from_code`).
I thought this was kind of like cheating and that it might not resolve
this part of Micha's
[comment](https://github.com/astral-sh/ruff/pull/18391#issuecomment-2933764275):
> because we can't add Rule to Diagnostic or **have it anywhere in our
shared rendering logic**
but after looking again, the only remaining `Rule` conversion in
rendering code is for the SARIF output format. The other two non-test
`Rule` conversions are for caching and writing a fix summary, which I
don't think fall into the shared rendering logic. That leaves the SARIF
format as the only real problem, but maybe we can delay that for now.
The motivation here is that we won't be able to store a `Rule` on the
new `Diagnostic` type, but we should be able to store a `NoqaCode`,
likely as a string.
## Test Plan
Existing tests
##
[Benchmarks](https://codspeed.io/astral-sh/ruff/branches/brent%2Fremove-to-rule)
Almost no perf regression, only -1% on
`linter/default-rules[large/dataset.py]`.
---------
Co-authored-by: Micha Reiser <micha@reiser.io>
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## Summary
Fixes#8334.
`Display` has been implemented for `ruff_workspace::Settings`, which
gives a much nicer and more readable output to `--show-settings`.
Internally, a `display_settings` utility macro has been implemented to
reduce the boilerplate of the display code.
### Work to be done
- [x] A lot of formatting for `Vec<_>` and `HashSet<_>` types have been
stubbed out, using `Debug` as a fallback. There should be a way to add
generic formatting support for these types as a modifier in
`display_settings`.
- [x] Several complex types were also stubbed out and need proper
`Display` implementations rather than falling back on `Debug`.
- [x] An open question needs to be answered: how important is it that
the output be valid TOML? Some types in settings, such as a hash-map
from a glob pattern to a multi-variant enum, will be hard to rework into
valid _and_ readable TOML.
- [x] Tests need to be implemented.
## Test Plan
Tests consist of a snapshot test for the default `--show-settings`
output and a doctest for `display_settings!`.
