Adopt towncrier for changelogs

[poljar]

This closes #5999.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.95%. Comparing base (c253114) to head (8e5d477).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6543      +/-   ##
==========================================
+ Coverage   89.92%   89.95%   +0.02%     
==========================================
  Files         381      381              
  Lines      107718   107718              
  Branches   107718   107718              
==========================================
+ Hits        96870    96894      +24     
+ Misses       7173     7158      -15     
+ Partials     3675     3666       -9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[codspeed-hq]

Merging this PR will degrade performance by 48.79%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 1 regressed benchmark
✅ 49 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	Restore session [memory store]	114.2 ms	223 ms	-48.79%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing poljar/towncrier (8e5d477) with main (c253114)}

[andybalaam]

Looks good, and I think it will work with https://codeberg.org/andybalaam/changelog-builder too. Grab me if not.

[poljar]

Looks good, and I think it will work with https://codeberg.org/andybalaam/changelog-builder too. Grab me if not.

Yeah I want to merge this and then switch to an xtask for the changelog generation.

[richvdh]

I think you probably want to remove the ## [Unreleased] - ReleaseDate headers from the changelogs?

[poljar]

Ah indeed, I'll do that while migrating some changelog entries that snuck in between the release and the merger of this PR.