Add `mypy` type check to `annotation/`

[Jiaqi-Lv]

• [x] dsl.py
• [x] storage.py

Had to edit some files in utils/ and and tools/ because they were failing mypy. Also added a few additional pytests.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.89%. Comparing base (a66fa19) to head (fea465b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #806 +/- ## ======================================== Coverage 99.89% 99.89% ======================================== Files 69 69 Lines 8577 8650 +73 Branches 1641 1653 +12 ======================================== + Hits 8568 8641 +73 Misses 1 1 Partials 8 8 ```

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