[WIP] Implementation of LU Decomposition

[rabbull]

This PR implements LU decomposition by enhancing gaussian_elimination to support step-by-step recording of row operations. These recorded steps can then be replayed on an identity matrix to construct the L matrix.

Four new methods are introduced:

• gaussian_elimination_ex: An extended version of Gaussian elimination that includes an option to record the steps performed during row operations. The existing gaussian_elimination method now serves as a wrapper for this function.
• lu_decomposition: Computes the LU decomposition of a matrix. This method returns the lower triangular matrix L, the upper triangular matrix U, and a permutation vector pv (if row permutations occur during Gaussian elimination).
• lu_decomposition_in_place: A more memory-efficient variant of lu_decomposition. Instead of returning U, it modifies the original matrix (self) in place to represent U.
• permute_rows: A utility function that applies a permutation vector pv to a matrix, enabling consistent handling of row permutations.

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