Update to [Rust
1.74](https://blog.rust-lang.org/2023/11/16/Rust-1.74.0.html) and use
the new clippy lints table.
The update itself introduced a new clippy lint about superfluous hashes
in raw strings, which got removed.
I moved our lint config from `rustflags` to the newly stabilized
[workspace.lints](https://doc.rust-lang.org/stable/cargo/reference/workspaces.html#the-lints-table).
One consequence is that we have to `unsafe_code = "warn"` instead of
"forbid" because the latter now actually bans unsafe code:
```
error[E0453]: allow(unsafe_code) incompatible with previous forbid
--> crates/ruff_source_file/src/newlines.rs:62:17
|
62 | #[allow(unsafe_code)]
| ^^^^^^^^^^^ overruled by previous forbid
|
= note: `forbid` lint level was set on command line
```
---------
Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>
## Summary
This exists to power a test, but it ends up affecting the behavior of
all files in the directory. Namely, it means that these files _aren't_
excluded when you format or lint them directly, since in that case, Ruff
will fall back to looking at the `pyproject.toml` in
`crates/ruff_linter/resources/test/fixtures`, which _doesn't_ exclude
these files, unlike our top-level `pyproject.toml`.
## Summary
This PR adds a new `lint` section to the configuration that groups all linter-specific settings. The existing top-level configurations continue to work without any warning because the `lint.*` settings are experimental.
The configuration merges the top level and `lint.*` settings where the settings in `lint` have higher precedence (override the top-level settings). The reasoning behind this is that the settings in `lint.` are more specific and more specific settings should override less specific settings.
I decided against showing the new `lint.*` options on our website because it would make the page extremely long (it's technically easy to do, just attribute `lint` with `[option_group`]). We may want to explore adding an `alias` field to the `option` attribute and show the alias on the website along with its regular name.
## Test Plan
* I added new integration tests
* I verified that the generated `options.md` is identical
* Verified the default settings in the playground

## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
Extends work in #7046 (some relevant discussion there)
Changes:
- All nursery rules are now referred to as preview rules
- Documentation for the nursery is updated to describe preview
- Adds a "PREVIEW" selector for preview rules
- This is primarily to allow `--preview --ignore PREVIEW --extend-select
FOO001,BAR200`
- Using `--preview` enables preview rules that match selectors
Notable decisions:
- Preview rules are not selectable by their rule code without enabling
preview
- Retains the "NURSERY" selector for backwards compatibility
- Nursery rules are selectable by their rule code for backwards
compatiblity
Additional work:
- Selection of preview rules without the "--preview" flag should display
a warning
- Use of deprecated nursery selection behavior should display a warning
- Nursery selection should be removed after some time
## Test Plan
<!-- How was it tested? -->
Manual confirmation (i.e. we don't have an preview rules yet just
nursery rules so I added a preview rule for manual testing)
New unit tests
---------
Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>