feat: drop support for Python 3.9

[bellini666]

Dropping support for Python 3.9, which has EOLed, and removing a lot of unneeded code that we had to workaround some of its limitations

[sourcery-ai]

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[botberry]

Thanks for adding the RELEASE.md file!

Here's a preview of the changelog:

---

This release drops support for Python 3.9, which reached its end-of-life (EOL)
in October 2025. The minimum supported Python version is now 3.10.

We strongly recommend upgrading to Python 3.10 or a newer version, as older
versions are no longer maintained and may contain security vulnerabilities.

Here's the tweet text:

🆕 Release (next) is out! Thanks to @_bellini666 for the PR 👏

Get it here 👉 https://strawberry.rocks/release/(next)

[botberry]

Thanks for adding the RELEASE.md file!

Here's a preview of the changelog:

---

This release drops support for Python 3.9, which reached its end-of-life (EOL)
in October 2025. The minimum supported Python version is now 3.10.

We strongly recommend upgrading to Python 3.10 or a newer version, as older
versions are no longer maintained and may contain security vulnerabilities.

Here's the tweet text:

🆕 Release (next) is out! Thanks to @_bellini666 for the PR 👏

Get it here 👉 https://strawberry.rocks/release/(next)

[botberry]

Apollo Federation Subgraph Compatibility Results

Federation 1 Support	Federation 2 Support
_service 🟢 @key (single) 🟢 @key (multi) 🟢 @key (composite) 🟢 repeatable @key 🟢 @requires 🟢 @provides 🟢 federated tracing 🔲	@link 🟢 @shareable 🟢 @tag 🟢 @override 🟢 @inaccessible 🟢 @composeDirective 🟢 @interfaceObject 🟢

Learn more:

• Apollo Federation Subgraph Specification
• Compatibility Tests

[codecov]

Codecov Report

❌ Patch coverage is 98.07692% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.41%. Comparing base (f98f2e7) to head (d2be958).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4018      +/-   ##
==========================================
+ Coverage   94.29%   94.41%   +0.12%     
==========================================
  Files         533      532       -1     
  Lines       34893    34773     -120     
  Branches     1846     1828      -18     
==========================================
- Hits        32901    32831      -70     
+ Misses       1687     1647      -40     
+ Partials      305      295      -10     

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[codspeed-hq]

CodSpeed Performance Report

Merging #4018 will not alter performance

_{Comparing drop-py-39 (d2be958) with main (f98f2e7)}

Summary

✅ 26 untouched

[DoctorJohn]

Do we still need this check? 🤔

[bellini666]

According to the comment, there's a small issue on 3.10 that got fixed on 3.10.1, so yes.

Like, nobody should be using 3.10.0 anymore, and should be at least on 3.10.1. But, who knows 🤣