* Infer target-version from project metadata
* Fix requires-python with ">=3.8.16"
* Load requires-python at runtime
* Use upstream VersionSpecifiers
* Add debug information when parsing ruff.toml
* Display debug only if target_version is not set
* Bump pep440-rs to add impl Error for Pep440Error
# Summary
We need to support CR line endings (as opposed to LF and CRLF line endings, which are already supported). They're rare, but they do appear in Python code, and we tend to panic on any file that uses them.
Our `Locator` abstraction now supports CR line endings. However, Rust's `str#lines` implementation does _not_.
This PR adds a `UniversalNewlineIterator` implementation that respects all of CR, LF, and CRLF line endings, and plugs it into most of the `.lines()` call sites.
As an alternative design, it could be nice if we could leverage `Locator` for this. We've already computed all of the line endings, so we could probably iterate much more efficiently?
# Test Plan
Largely relying on automated testing, however, also ran over some known failure cases, like #3404.
This PR sets up an "ecosystem" check as an optional part of the CI step for pull requests. The primary piece of this is a new script in `scripts/check_ecosystem.py` which takes two ruff binaries as input and compares their outputs against a corpus of open-source code in parallel. I used ruff's `text` reporting format and stdlib's `difflib` (rather than JSON output and jsondiffs) to avoid adding another dependency. There is a new ecosystem-comment workflow to add a comment to the PR (see [this link](https://securitylab.github.com/research/github-actions-preventing-pwn-requests/) which explains why it needs to be done as a new workflow for security reasons).
## Summary
This PR moves `Diagnostic`, `DiagnosticKind`, and `Fix` into their own crate, which will enable us to further split up Ruff, since sub-linter crates (which need to implement functions that return `Diagnostic`) can now depend on `ruff_diagnostics` rather than Ruff.
