dg1d: refactor lgl and glgl modules

Unify interface for LGL and GLGL rules and update SpectralElement accordingly:

• most routine should just work with one argument Npts
• add more doc strings
• remove unused methods linear_dependency_matrix and expansion_matrix
• remove unused fields of SpectralElement

added refactor label

added 3 commits

• b3d8f8c6 - fixup type constraints on differentiate
• 2f9d1a0f - rm unused
• b1e2a627 - update reftests

Compare with previous version

Some reftests needed to be updated, because inner_product now uses the mass matrix for evaluation, and for :lgl it is computed exactly whereas before we used the lumping approximation.

enabled an automatic merge when the pipeline for b1e2a627 succeeds

aborted the automatic merge because source branch was updated

added 1 commit

• 73c84f38 - update more reftests

Compare with previous version

enabled an automatic merge when the pipeline for 73c84f38 succeeds

added update reftest label

merged

mentioned in commit a940bcc6