Chore: Clippy Code Cleanup Story Ticket

[jferrant]

This is a main story ticket for cleaning up the stacks-blockchain repo by addressing clippy errors throughout the entire code base.

To run clippy on just the offending package : cargo clippy -p PACKAGE_TO_CHECK --no-deps

Subtasks include:

• [x] #3935
• [x] #3936
• [x] #3937
• [x] #3938
• [ ] #3939
• [ ] #3940
• [ ] #3941
• [x] #3979
• [x] #4020
• [x] #4021
• [x] #4022
• [ ] #4023
• [ ] #4024
• [ ] #4025
• [ ] #3942
• [ ] #4804

[obycode]

I'd suggest we use -- -D warnings to treat the warnings as errors too.

[obycode]

Adding a note here that once develop is merged into next, including the clippy checks, we should enable those checks for PRs against next as well (it's currently only enabled for PRs against develop).