docs(examples): add tutorial for extracting coordinates from multivectors

[utiberious]

Summary

Adds a tutorial example showing the various ways to extract scalar coefficients from a multivector, addressing the question in issue 483.

Replaces the closed PR 547 which incorrectly added a new method shadowing the existing components().

Fixes #483

Methods demonstrated

• blade_coefs(blade_list): get coefficients for specific basis blades (the primary tool for numeric work)
• components(): split into single-blade Mv objects
• get_coefs(grade): coefficients of all blades of a specific grade
• scalar() / get_grade(r): extract specific grades
• Symbolic coordinates with subs() and float() for numeric conversion

Changes

• examples/Terminal/extracting_coords.py: New tutorial example

Test plan

• python examples/Terminal/extracting_coords.py runs without errors
• No code changes, example only

[utensil]

Thanks for this! Two things:

1. The issue specifically asked for this to be in the tutorial docs (https://galgebra.readthedocs.io/en/latest/tutorials/algebra.html), not just a terminal example. Could you add it there instead?
2. Line 76: [float(v) for v in vals] shadows the v multivector from earlier. Rename to x or val.

Introduction to using GAlgebra — galgebra documentation

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[utiberious]

Addressed both:

1. Added an "Extracting coordinates" section to examples/ipython/tutorial_algebra.ipynb (the readthedocs tutorial). It covers:

   • blade_coefs([ex, ey, ez]) for specific basis blades
   • float() for numeric conversion
   • components() for single-blade decomposition
   • blade_coefs() (no args), scalar(), and grade(k) for general multivectors

2. Fixed variable shadowing: float(v) -> float(val) in the terminal example.

All 24 notebook cells pass nbval. Pushed in 78976c3.