Bump pyarrow from 19.0.1 to 21.0.0

Bumps [pyarrow](https://github.com/apache/arrow) from 19.0.1 to 21.0.0.
- [Release notes](https://github.com/apache/arrow/releases)
- [Commits](apache/arrow@apache-arrow-19.0.1...apache-arrow-21.0.0)

---
updated-dependencies:
- dependency-name: pyarrow
  dependency-version: 21.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -14,5 +14,5 @@ netcdf4==1.7.2
 h5netcdf==1.6.4
 impactlab-tools==0.6.0
 p_tqdm==1.4.2
-pyarrow==19.0.1
+pyarrow==21.0.0
 numcodecs==0.15.1