Clean up test suite

[vemv]

Commits:

• Remove unused provides in tests
  • These can be confusing, since Buttercup doesn't use them
• Use it more
  • This ensures their execution is displayed on CI logs.
• Settle on *tests.el naming
• Add a standard header suggesting it blocks
• Bump some copyright years
• Run test suite on Emacs 29
  • We already were (via master), but now we will run 29 stable and 29 master (which will become 30 at some point, I guess)
• Cover cider-format-connection-params
  • Part of [Emacs 29.1] Error when starting Cider (wrong-number-of-arguments (1 . 1) 0) #3402
• Fix cider-format-connection-params edge case for Emacs 29
  • Closes [Emacs 29.1] Error when starting Cider (wrong-number-of-arguments (1 . 1) 0) #3402

Cheers - V

[vemv]

Finally I added a fix for #3402 . It's a bit unrelated to this PR's theme, but small enough to let it slip (hopefully)

[vemv]

Avoids this code path https://github.com/emacs-mirror/emacs/blame/d3dae88e6cc8118c875957ba0347be9599014b34/lisp/format-spec.el#L110

e.g. if the user had a function named clj, we change it from symbol to string, so that it's not functionp anymore.

I was able to reproduce this scenario on CI, verifying that the tests would fail if we remove this fix.

[bbatsov]

Nice improvements!