[Tech Debt] [python] Remove setuptools<82 constraint after apache-flink upgrades to apache-beam>=2.66.0

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/flink-agents/issues) and found nothing similar.

### Description

### Problem

`setuptools 82.0.0` (released Feb 8, 2026) removed `pkg_resources` module entirely. `apache-beam<2.66.0` still uses `pkg_resources` in its `setup.py` ([source](https://github.com/apache/beam/blob/v2.65.0/sdks/python/setup.py)), so building `apache-beam` from source fails with:

```
ModuleNotFoundError: No module named 'pkg_resources'
```

Currently all `apache-flink` depends on `apache-beam <= 2.61.0`, which is affected.

### Current Workaround

We added `setuptools<82` constraints in `pyproject.toml` to pin setuptools to a version
that still includes `pkg_resources`:
- `[build-system] requires`: `setuptools>=75.3,<82`
- `[project] dependencies`: `setuptools>=75.3,<82`
- `[tool.uv.extra-build-dependencies]`: `apache-beam = ["setuptools<82"]`

PR: https://github.com/apache/flink-agents/pull/526

### Long Term Solution

`apache-beam>=2.66.0` removed `pkg_resources` usage from `setup.py`([PR #35153](https://github.com/apache/beam/pull/35153)).
Once `apache-flink` upgrades its `apache-beam` dependency to `>=2.66.0`, we can remove all `setuptools<82` constraints.

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start in pyproject.toml, reviewing the apache-flink dependency and the three setuptools<82 constraints under [build-system], [project], and [tool.uv.extra-build-dependencies]. Confirm apache-flink uses apache-beam>=2.66.0, then remove the constraints and verify that the dependency build no longer requires the workaround.

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