Add various Poly helper methods

[mhostetter]

Summary

What does this change do, and why?

Type

• Fix (bug / correctness)
• Feature (new capability)
• Performance
• Docs / tooling / CI
• Refactor (no behavior change)

Release notes

• Not user-facing (no entry needed)
• Added entry to docs/release-notes/unreleased.md

Testing

• Added/updated tests
• pytest (command / notes):
• Other validation (benchmarks, docs build, examples):

Backwards compatibility

• No breaking changes
• Potentially breaking (describe + rationale)

Checklist

• PR base branch is develop
• CI is green
• Docs/docstrings updated where appropriate

[codecov]

Codecov Report

❌ Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.21%. Comparing base (eca60fb) to head (946af98).

Files with missing lines	Patch %	Lines
src/galois/_polys/_poly.py	95.23%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #652      +/-   ##
===========================================
- Coverage    95.22%   95.21%   -0.02%     
===========================================
  Files           48       48              
  Lines         6244     6264      +20     
===========================================
+ Hits          5946     5964      +18     
- Misses         298      300       +2     

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[mhostetter]

Combining with #634