chore: add Python 3.13 support

[codecov[bot]]

Codecov Report

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

Project coverage is 92.44%. Comparing base (d8e10c7) to head (d11fbc9). Report is 41 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #95 +/- ## ========================================== + Coverage 90.55% 92.44% +1.88% ========================================== Files 8 12 +4 Lines 180 463 +283 ========================================== + Hits 163 428 +265 - Misses 17 35 +18 ``` | [Flag](https://app.codecov.io/gh/open-feature/python-sdk-contrib/pull/95/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-feature) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/open-feature/python-sdk-contrib/pull/95/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-feature) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-feature#carryforward-flags-in-the-pull-request-comment) to find out more.

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[gruebel]

ok, this needs to wait for gRPC to support 3.13 https://github.com/grpc/grpc/issues/34922

[beeme1mr]

@gruebel, it looks like gRPC now supports Python 3.13!

[gruebel]

Nice, giving it a try.

[federicobond]

Will this work without allow-prereleases: true now?

[gruebel]

Yeah, it should work without now.