Add unused_impl lint

[vogelbirb]

Added exceptions (mostly #![allow(clippy::unused_impl)]) to the following lints:

• impl
• into_iter_without_iter
• mismatching_type_param_order
• multiple_inherent_impl_cfg
• needless_lifetimes
• needless_maybe_sized
• too_long_first_doc_paragraph
• doc_comments
• unknown_clippy_lints
  • Suggestion changed to clippy::unused_impl from clippy::unused_self

fixes #16758
changelog: new lint: [unused_impl]

[rustbot]

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[github-actions]

Lintcheck changes for 612b2b0

Lint	Added	Removed	Changed
clippy::unused_impl	13	0	0

This comment will be updated if you push new changes

[samueltardieu]

Lintcheck shows false positives. An empty impl block with comments or #[cfg] should not be linted.

Please write a meaningful PR message, the current one looks like LLM verbose output.

When the .fixed file of an unrelated test still triggers the lint, use #![expect] instead of #![allow].

View changes since this review

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.