Partition-of-unity constraints must hold for the generated tables JuliaFEM ships,
not a parallel copy pulled via relative paths.
- Replace includes with `using JuliaFEM`.
New 31-line test for partition of unity property:
- Tests that sum of basis functions equals 1.0
- Covers Seg2, Tri3, Quad4 elements
- Included in test/basis/runtests.jl
- Validates fundamental basis function property
Ensures basis functions satisfy partition of unity requirement.