Release 0.7.3

SOLVAX 0.7.3 adds block_thomas_truncated_fn_with_residual. The API evaluates the retained tail-eliminated Schur residual directly from pivoted LU factors as L(Ux)-P b, without reconstructing another block or materializing diagonal bands. Multi-RHS callers may select one residual channel to limit diagnostic overhead.

This is the minimum SOLVAX version required by NTX’s bounded-memory solver migration. On the measured NTX prepared solve, it preserves coefficient parity through N_xi=140, reduces CPU/GPU temporary memory, and improves warm CPU/GPU runtime; cold compilation remains slower and is reported separately by NTX.