- restore the 8 .yml.disabled workflows back to .yml
- drop the gcc-13 gcov coverage matrix row; native clang-20 llvm-cov is
now the only codecov reporter
- update minimal_matrix indices to match
- remove the TEMP narrowing block that filtered to just the llvm-cov row
- log line says '7 configs (build x6 + clang-20 llvm-cov coverage)' to
reflect the new shape
renames every non-nix workflow to .yml.disabled so they stop firing on
PR pushes while we iterate on the llvm-cov coverage row. MUST be
reverted before merging to dev.
