2D Tilt Correction

[hpparvi]

This PR introduces specreduce.tilt_correction.TiltCorrection and specreduce.tilt_solution.TiltSolution classes. The TiltCorrection class can be used to estimate the 2D tilt distortion as an astropy Polynomial2D model from (optionally multiple) arc frame(s), while the TiltSolution class can be used to access the tilt-corrected to detector mapping and its inverse, resample science frames, or export the tilt model as a GWCS object.

LLM usage: I've used Claude Code (Opus 4.6) to revise the language in the documentation, revise the docstrings, find and fix several bugs, improve the documentation of some parts of the code, and to implement the TiltSolution._calculate_inverse method (that I had implemented myself earlier, then removed since I considered it unnecessary, until I realized it may be quite necessary indeed in the future, but was too lazy to find the commit where I still had it). Additionally, I used Grammarly to fix the grammar in this PR description.

[codecov]

Codecov Report

❌ Patch coverage is 94.01408% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.93%. Comparing base (dd2fbe4) to head (3dae516).

Files with missing lines	Patch %	Lines
specreduce/tilt_correction.py	93.71%	10 Missing ⚠️
specreduce/tilt_solution.py	94.40%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #303      +/-   ##
==========================================
+ Coverage   90.45%   90.93%   +0.47%     
==========================================
  Files          16       18       +2     
  Lines        1855     2139     +284     
==========================================
+ Hits         1678     1945     +267     
- Misses        177      194      +17     

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