Add migratory deprecation to munitTimeout

[armanbilge]

This is a followup to #233. The problem is anyone who was overriding munitTimeout to be longer than 30 seconds will get tripped up by the new munitIOTimeout which will fire first.

So this PR adds a @deprecatedOverriding annotation to munitTimeout to indicate that munitIOTimeout should be used instead. It's not a real deprecation, but it's unlikely a user will actually want to override munitTimeout.

@bpholt also suggests we can write a scalafix for this. We'd have to make sure that the test suite inherits from CatsEffectSuite before applying the rewrite. Any volunteers? 😁

[armanbilge]

Btw, I'm not dead set on the deprecation. Mostly want to open a discussion about this issue, and adding a deprecation notice is much easier than writing a scalafix 😅

[bpholt]

I may have time to work on a scalafix next week! Happy to have someone else take that on if anyone is interested though.

[danicheg]

Like this idea 👍