Order vector tp

[inducer]

• Still waiting on a test, currently being made by Claude (maybe?)

cc @ShawnL00

This makes inducer/meshmode#494 way neater.

[Copilot]

Pull request overview

This PR generalizes modal-decay utilities to support tensor-product bases by introducing a basis-aware “degree vector” and a new interpolation error coefficient estimator matrix API, along with a new regression test covering simplex and hypercube shapes.

Changes:

• Add degree_vector() (with simplex/tensor-product implementations) and interp_error_coefficient_estimator_matrix(), and deprecate simplex_interp_error_coefficient_estimator_matrix.
• Expose a new public SimplexBasis base class (renaming the previous private _SimplexBasis).
• Add a new test validating that the estimator tracks actual interpolation error across shapes and smoothness classes.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

File	Description
modepy/test/test_tools.py	Adds a new test for interp_error_coefficient_estimator_matrix across simplex/hypercube shapes.
modepy/modes.py	Renames _SimplexBasis to public SimplexBasis and updates internal subclasses accordingly; updates docs section.
modepy/modal_decay.py	Adds degree_vector singledispatch, adds new estimator-matrix API, and deprecates the simplex-only helper.
modepy/__init__.py	Exports SimplexBasis from the top-level package.

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[alexfikl]

Left a little nitpick, otherwise looks good to me!