fix(deps): Update dependency pyarrow to v21 (#175)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [pyarrow](https://redirect.github.com/apache/arrow) | major | `==20.0.0` -> `==21.0.0` |

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requirements.txt

@@ -2,5 +2,5 @@ black==25.1.0
 grpcio-tools==1.74.0
 grpcio==1.74.0
 protobuf>=6.30.0
-pyarrow==20.0.0
+pyarrow==21.0.0
 pytest==8.4.1