staging: add `[workspace.lints]` to manifest

[epilys]

Summary of the PR

This PR enables all crates of the staging workspace to share lints. With 1.74 it is now possible to define them in Cargo.toml.

Note: In older versions you'll simply get a "warning: unused manifest key" when using cargo.

Requirements

Before submitting your PR, please make sure you addressed the following requirements:

• [x] All commits in this PR are signed (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [x] Any newly added unsafe code is properly documented.