Improve interface

[duembgen]

This pull request introduces improvements to the matrix rank manipulation utilities in cert_tools/linalg_tools.py and enhances the reporting of solver status in cert_tools/sdp_solvers.py. The main changes include the addition of a new function for extracting lower-rank solutions from positive semidefinite matrices and improved reporting and typing.

Matrix rank manipulation utilities:

• Added a new function extract_lower_rank_solution to cert_tools/linalg_tools.py that attempts to reduce the rank of a given positive semidefinite matrix by one, using nullspace computations and iterative updates.
• Updated the return type of rank_project to explicitly return a tuple of a NumPy array and a dictionary, and ensured the projected matrix is returned as a NumPy array.
• Added an import of warnings to support warning messages in new functionality.

Solver status reporting:

• In cert_tools/sdp_solvers.py, added extraction of solver statistics and success status after solving, and included this information in the returned info dictionary for low-rank SDP solves.