Revert Pyupgrade Pep 604 Typing Rewrites

[collindutter]

Reverts pyupgrade's pep 604 typing rewrites which causes issues with #561 on versions greater than python 3.9.

Thank goodness for regexes.

[collindutter]

So this is really only an issue in the context of #561 when the union syntax is used in a field since those are the types that are resolved when building a schema.

Feels kind of weird to require Union for fields, but allow | syntax elsewhere. Should we just drop 3.9?

[collindutter]

Relevant

fastapi/typer#371

https://blog.derlin.ch/python-type-hints-and-future-annotations

[SavagePencil]

Two questions that do not impact approval but want addressed before we move forward with this one.

[SavagePencil]

bless this mess

[andrewfrench]

So this is really only an issue in the context of #561 when the union syntax is used in a field since those are the types that are resolved when building a schema.

Feels kind of weird to require Union for fields, but allow | syntax elsewhere. Should we just drop 3.9?

That does feel weird, and maybe would be easier to drop 3.9. It'd be an easier decision if we had any idea what the version breakdown was among users. I found these survey results from Jetbrains (the 2023 survey results aren't available yet) implying 3.9 has a pretty large share, but clearly pretty out of date by now as it only includes versions as high as 3.10.

[collindutter]

Another option could be to go all in on the revert so consistent throughout. I only reverted to T | None to Optional[T]. We could also revert T | U | V to Union[T, U, V], but this would undo a decision made in #226.

Dropping 3.9 feels wrong, also I think 3.10 still has some issues with | syntax.

[andrewfrench]

Nothing worth blocking approval over but several unused Optional imports added here.

The question around 3.9 support generally is worth discussing but can happen outside this PR.