Apply PEP 604 union type syntax codemod

[Balandat]

This codemods all Optional[X] type definitions to use the PEP 604 syntax X | None instead.

[codecov[bot]]

Codecov Report

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

Project coverage is 99.98%. Comparing base (68faeff) to head (71b14e0). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2561 +/- ## ========================================== - Coverage 99.98% 99.98% -0.01% ========================================== Files 193 193 Lines 17111 17071 -40 ========================================== - Hits 17108 17068 -40 Misses 3 3 ```

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@Balandat has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

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This pull request was exported from Phabricator. Differential Revision: D63733395

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This pull request was exported from Phabricator. Differential Revision: D63733395

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@Balandat merged this pull request in pytorch/botorch@a0a2c0509dbbeec547a65f16cb0cb8d5b19fd7f1.