Fix Union entry point discovery on Python <3.12

[Copilot]

databind.core.union.iter_entry_points() called importlib.metadata.entry_points(group=...), which is not supported on older Python versions (e.g. 3.9/3.11), causing runtime failures when resolving EntrypointUnionMembers. This change restores cross-version compatibility without raising the minimum supported Python version.

• Entry point compatibility fix

  • Updated iter_entry_points(group) to call entry_points() without arguments.
  • Uses modern API when available: entry_points().select(group=...).
  • Falls back to legacy mapping-style return values via entry_points().get(group, ()).

• Regression coverage

  • Added focused tests for both importlib metadata behaviors:
    • selectable EntryPoints object (.select(group=...))
    • mapping-style result ({group: [...]})

def iter_entry_points(group: str) -> t.Iterator[EntryPoint]:
    eps = entry_points()
    if hasattr(eps, "select"):
        return iter(eps.select(group=group))
    return iter(eps.get(group, ()))

[Copilot]

Pull request overview

Fixes databind.core.union.iter_entry_points() to work across supported Python versions by avoiding the unsupported entry_points(group=...) call on Python < 3.12, while also removing the now-unneeded pkg_resources/setuptools fallback path.

Changes:

• Update iter_entry_points(group) to call entry_points() without arguments and select the group via .select() when available, otherwise fall back to mapping-style results.
• Add regression tests covering both “selectable” and “mapping-style” entry_points() return shapes.
• Drop the setuptools runtime dependency (and types-setuptools dev dependency) since pkg_resources is no longer used.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
databind/src/databind/core/union.py	Reworks entry point enumeration to be compatible with older importlib.metadata APIs.
databind/src/databind/core/tests/union_test.py	Adds regression tests for both entry_points().select() and mapping-style entry_points() behaviors.
databind/pyproject.toml	Removes conditional runtime dependency on setuptools for Python < 3.9.
pyproject.toml	Removes types-setuptools from the workspace dev dependency group.
uv.lock	Reflects dependency removals (setuptools, types-setuptools) in the lockfile.
.changelog/_unreleased.toml	Adds an unreleased changelog entry describing the fix and dependency removal.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.