Just some minor cleanup and reorganization in the script folder.
Wanted to tidy up all the different scripts we have.

Move the `contracts` directory to `src` and then move
the tests into a top level `test` dir so that its
standard foundry style for a repo.

This is going to break any in flight PRs so worth trying
to get in relatively quickly, will be no fun to rebase a
bunch of PRs.

Will need to follow up with another commit that bumps the
patch versions.

* Begin simple invariant docgen script

* Support Echidna tests in invariant docgen

* Use custom natspec tags for invariant doc comments

* Handle multi-line headers for linting purposes

* Restack

* Upstack

* New doc

* New doc

* Add test file name to link in docgen script

* Relative URL path

* Use `path.join`

* Add task to `contracts-bedrock` workflow to check diff of `invariant-docs`

* Generate a table of contents for invariant docs