Make the SVD sweep budget configurable #156

What: The one-sided Jacobi SVD runs a hardcoded max_sweeps = 60. Every other iterative routine takes a budget from config; SVD should too, and it should be documented. Add it to the SVD's settings with 60 as the default so existing behaviour is unchanged.

Where: crates/multicalc/src/linear_algebra/svd.rs.

How to test: cargo test -p multicalc; confirm the default matches today's results.