GH-47930: Update Rust support status for Avro format in documentation

[jecsand838]

Rationale for this change

The Third‑Party Data Formats Implementation Status table currently leaves the Rust column blank for Avro. As of arrow-rs 57.0.0 (tagged 2025‑10‑19), Arrow’s Rust implementation ships an official arrow-avro crate that provides both read and write support.

References:

• arrow‑rs 57.0.0 release notes: "Added Avro support (new arrow-avro crate)"
• Add Avro Support arrow-rs#4886 is closed.
• arrow_avro crate docs describing reader + writer support.
• GitHub Issue: [Docs][Rust] Mark Avro external data format status as R/W for Rust #47930

What changes are included in this PR?

• Edited the "Third‑Party Data Formats" table's Avro Rust cell to R/W in the `docs/source/status.rst file.

Are these changes tested?

N/A, docs‑only change. The Sphinx docs build in CI will validate the page renders correctly.

Are there any user-facing changes?

Yes. The published Implementation Status page will show Avro as R/W for Rust under Third‑Party Data Formats.

• GitHub Issue: [Docs][Rust] Mark Avro external data format status as R/W for Rust #47930

[github-actions]

⚠️ GitHub issue #47930 has been automatically assigned in GitHub to PR creator.

[mbrobbel]

🎉

[alamb]

Thank you @jecsand838 @martin-g and @mbrobbel

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit 7623887.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 8 possible false positives for unstable benchmarks that are known to sometimes produce them.