[clippy] reinstate clippy

[sphinxc0re]

Yes please. Just for statistics:

[ddd-mtl]

This is what we agreed in MTL hodlpodl back in october:

"We agree that we dont want any Warn status for lints. We decided status of lints by category: Our clippy configuration:

• clippy::nursery: Allow (unstable)
• clippy::style Allow (arbitrary - controversial)
• clippy::complexity Deny (nobody likes complexity)
• clippy::perf Deny (everybody like performances)
• clippy::cargo Allow (just one anyway)
• clippy::correctness Deny (code that is just outright wrong or very very useless)

Try out cyclomatic complexity max count number: 25?

After 50-ish times the same attribute is used to manually skip a lint, than we can put that up for a change request to change the configuration. (Send it to the Clippy Committee). Might also need to reform the Clippy Committee to update clippy version. We currently use a specific version. This is for all core dev team 'controlled' repos."

[thedavidmeister]

yes i think we should actually implement what we said at MTL