change: Replace usage of Optional and Union in AutoQASM type hints

[rmshaffer]

Issue #, if available: Convert all AutoQASM code to use new-style Python annotations (via from __future__ import annotations)

Description of changes: Replace usage of Optional and Union in type hints with the more modern syntax.

Testing done: tox passes.

Merge Checklist

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[codecov[bot]]

Codecov Report

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

Project coverage is 100.00%. Comparing base (ff34cd4) to head (a95e5de).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## feature/autoqasm #925 +/- ## ================================================== Coverage 100.00% 100.00% ================================================== Files 170 170 Lines 10487 10495 +8 Branches 2248 2248 ================================================== + Hits 10487 10495 +8 ```

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