Wrap fixed-size Eigen values as MATLAB arrays

[ProfFan]

Summary

• recognize MatrixN, MatrixMN, MatrixNxM, and VectorN aliases as fixed-size Eigen values in MATLAB codegen
• emit MATLAB double-array dispatch with fixed dimensions when the alias spelling is unambiguous
• add dimension-checked C++ conversion helpers for fixed-size Eigen inputs and outputs
• cover constructors, methods, properties, pairs, optionals, and rectangular matrices

Validation

• uv run pytest tests -q: 127 passed
• generated and compiled the complete GTSAM MATLAB wrapper with Octave 11.3
• Matrix3/Vector3 input-output round trip passed in Octave
• GTSAM MATLAB runner: 19 passed, 1 Octave script-local-function limitation; the remaining numerical derivative test passes when its helper is externalized

[dellaert]

Approved, but:

1. Could we do the unit test with a regular mechanism from this repo?
2. Could the Python code please throw an exception for non-const reference return values?