feat: add to_galsim method for Shear, Angle, CelestialCoord, and WCS classes

[beckermr]

This PR is a followup to #172 that takes care of

• Shears
• Angles
• CelestialCoords
• WCS objects

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing wcs-to-galsim (8c40ea5) with main (4cc222b)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 32 untouched benchmarks