[branch-55] chore: update version 55.2.0 and add changelog

[comphead]

Which issue does this PR close?

• Part of Release DataFusion 55.2.0 (patch) Release (Oct 2026) #25758.

Rationale for this change

Prepare the 55.2.0 patch release.

What changes are included in this PR?

Bumps the version to 55.2.0 in Cargo.toml, Cargo.lock and the docs, and adds dev/changelog/55.2.0.md.

What is the testing strategy for this PR?

No code changes. The changelog comes from dev/release/generate-changelog.py.

Are there any user-facing changes?

No.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.21%. Comparing base (ec74746) to head (f3136b5).

Additional details and impacted files

@@              Coverage Diff              @@
##           branch-55   #26037      +/-   ##
=============================================
- Coverage      81.21%   81.21%   -0.01%     
=============================================
  Files           1110     1110              
  Lines         388606   388606              
  Branches      388606   388606              
=============================================
- Hits          315614   315611       -3     
- Misses         54444    54445       +1     
- Partials       18548    18550       +2     

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[comphead]

Thanks @adriangb