[codex] Fix EllipseSample geometry sma cache reset

[hgao-astro]

Summary

Fixes #2105 by resetting EllipseGeometry attributes that are derived from sma when EllipseSample is constructed from an existing geometry and a new semimajor axis.

The root cause was that EllipseSample deep-copied the input geometry and overwrote geometry.sma, but left cached SMA-dependent values such as _area_factor, sector_angular_width, initial_polar_angle, and initial_polar_radius from the original geometry.

Changes

• Moved SMA-dependent geometry initialization into a private helper on EllipseGeometry.
• Called that helper after EllipseSample overrides the copied geometry sma.
• Added a regression test that compares the copied-and-overridden geometry against a freshly constructed geometry with the target sma.

Validation

• python -m pytest photutils/isophote/tests/test_sample.py
• python -m pytest photutils/isophote/tests/test_geometry.py photutils/isophote/tests/test_sample.py

[larrybradley]

Many thanks, @hgao-astro! I added a changelog entry for this bugfix and will merge when CI passes.