GH-47930: Update Rust support status for Avro format in documentation (#47931)

### 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)**"
- apache/arrow-rs#4886 is closed.
- `arrow_avro` crate docs describing reader + writer support.
- GitHub Issue: #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: #47930

Author: jecsand838

docs/source/status.rst

@@ -338,7 +338,7 @@ Third-Party Data Formats
 | Format                      | C++     | Java    | Go    | JS | C#    | Rust  | Julia | Swift |
 |                             |         |         |       |    |       |       |       |       |
 +=============================+=========+=========+=======+====+=======+=======+=======+=======+
-| Avro                        |         | R       | R     |    |       |       |       |       |
+| Avro                        |         | R       | R     |    |       | R/W   |       |       |
 +-----------------------------+---------+---------+-------+----+-------+-------+-------+-------+
 | CSV                         | R/W     | R (2)   | R/W   |    |       | R/W   | R/W   |       |
 +-----------------------------+---------+---------+-------+----+-------+-------+-------+-------+