feat(mv): add __rtruediv__ to support scalar/Mv expressions

[utiberious]

Summary

Adds __rtruediv__ to the Mv class so that expressions like 1/mv and scalar/mv work as expected, computing scalar * mv.inv().

Previously, 1/mv would raise a TypeError because Python's int.__truediv__ doesn't know how to handle Mv objects and Mv didn't implement __rtruediv__.

Fixes #512

Changes

• galgebra/mv.py: Add __rtruediv__ method that wraps the scalar as an Mv and multiplies by self.inv()
• test/test_mv.py: Add tests for 1/I, 2/v, and S(3)/I

Test plan

• pytest test/ -v passes
• Full CI with nbval notebooks passes

[utensil]

Tests look good. Checked against kingdon's approach — they use the same convention (A / mv = A * mv⁻¹) and their own test for this is actually just assert x.inv() == 1/x in 2D Euclidean, so this PR is already more thorough than the reference impl.

Two minor gaps worth noting: no test with a symbolic numerator (e.g. symbols('a') / v), and no non-Euclidean metric. Neither is blocking: kingdon doesn't cover them either.

[utiberious]

Thanks for the review! Added both suggested test cases:

• Symbolic numerator: symbols('a') / I
• Non-Euclidean metric: Minkowski-like g=[1, -1] with an invertible vector

Pushed in 5c1f0ac.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.95%. Comparing base (8f661e3) to head (5c1f0ac).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #543      +/-   ##
==========================================
- Coverage   78.93%   72.95%   -5.98%     
==========================================
  Files          19       19              
  Lines        4452     4452              
==========================================
- Hits         3514     3248     -266     
- Misses        938     1204     +266     

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[utensil]

Tests look good, thanks!

The coverage drop is likely a codecov artifact. Codecov itself says all modified lines are covered.