Add CI for profiling proof times

As we have more Lean newbies (such as myself) contributing, there's a good chance we'll see proofs that over-use `grind` as soon as it'll work, no matter the cost 😅 On the other hand, AI-derived proofs are often overly manual and post-processing them with "use more grind/etc"-style prompts seems beneficial to maintainability but can potentially run into the same issue.

In order to make it possible to review more efficiently (for example, entirely in-browser, rather than checking it out and manually profiling things) we should add an action that does profiling and reports useful data.

IIRC, @math-fehr mentioned he'd already played around with this?