Uniformize lemma names in the standard library

[utaal]

Current plan is:

• lemma_* prefix
• make lemmas associated functions when possible

[from the Verus meeting]

[parno]

I think we've largely done this? If so, should we keep this open as documentation or close it?

[utaal]

Closing is good!

Perhaps we can add a note in CONTRIBUTING.md about the convention?

[parno]

Done! (0684141)

[utaal]

Thank you!