Geometry modernization

[softmattertheory]

Extensive updates to geometry package:

• Significant performance improvements due to work estimator, new per-worker initialization and teardown.
• Field now supports complex numbers and complex matrices; distinct subtypes e.g. ScalarField, ComplexField, MatrixField etc.
• Additional finite elements for piecewise constant functions.
• Old quadrature routines removed in favor of the new quadrature routine, which is almost always faster.
• Meshtools now provides SelectionBuilder with star, link and closure.
• All function and method definitions provide signatures and use multiple dispatch.
• Functionals are more standardized; all now provide grade information.
• Code clean; functional definitions in subfolders.

[emmanuellfc]

This represents a significant improvement in Morpho development. I've been using and testing this branch in my own projects, and it has performed very well across the workflows I've tried. The performance gains are particularly noticeable, with a substantial improvement in overall runtime and responsiveness. From my testing so far, this branch feels like a major step forward.