Scheduler.py typing - remove allow_incomplete_defs

[fjetter]

This removes the flag for allow_incomplete_defs from scheduler.py. The step for allow_untyped_defs is rather minimal and concerns mostly Scheduler.__init__ but I stopped and leave this to another PR.

I do not intend do engage on a thorough review/feedback cycle unless something is horribly wrong. This is supposed to be a quick drive by to enable this flag. We can correct inaccurate types in follow up iterations. Spending too much time on this being open just increases risk of having merge conflicts, i.e. I would prefer addressing any review comments in a follow up

[crusaderky]

Some nits only. It should be just a matter of committing all suggestions and we're ready to go.

[crusaderky]

LGTM as soon as CI turns out green

[graingert]

github actions is down at the moment https://www.githubstatus.com/incidents/z3c6q056q332 so CI looks green but the mypy check didn't run

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

       25 files   -        1         25 suites   - 1   12h 52m 30s ⏱️ - 1h 35m 23s
  3 545 tests ±       0    3 432 ✔️ +       4     106 💤 ±  0    5 ❌  - 6  2 🔥 +2 
43 548 runs   - 1 297  41 319 ✔️  - 1 259  2 201 💤  - 35  26 ❌  - 5  2 🔥 +2 

For more details on these failures and errors, see this check.

Results for commit c420811. ± Comparison against base commit 215f379.

♻️ This comment has been updated with latest results.