Split `miden::note` into two modules

[Fumuran]

We should split miden::note module into two:

• Procedures related to the note currently being processed.
• Procedures for general note utilities.

The former we could call active_note, and the latter we could keep as just note.

Originally posted by @bobbinth in #1834 (comment)

[Fumuran]

I would wait until the #1876 is merged to avoid creating too much merge conflicts.

[bobbinth]

This should be unblocked now.