Nonrecursive contiguous subschedule

[erichulburd]

Rebases https://github.com/quil-lang/quilc/pull/693 which should fix tests.

Closes https://github.com/rigetti/quilc/issues/697

[stylewarning]

Both @stylewarning (me!) and @kilimanjaro will take a look.

[notmgsk]

I'm a bit sketched out by the original code, and also by the changes here.

Unnecessarily unfriendly language IMO

[braised-babbage]

I'm a bit sketched out by the original code, and also by the changes here.

Unnecessarily unfriendly language IMO

I didn't mean it as a strong statement, but rather that it's hard for me to look at the code (e.g. even as originally written) and say if it is correct or not (or if it would break if the logical scheduler code changed, etc).