Record propagator join normalization factors

[krystophny]

Summary

• optionally record each finite Lorentz-model join_ripples normalization factor before division
• include sequence, direction, column, old and new propagator tags, and passing dimensions in CSV output
• leave output disabled unless NEO2_JOIN_NORMALIZATION_FILE is set
• fail explicitly if requested diagnostic output cannot be created or written

The diagnostic does not change propagator matrices, normalization factors, flux-conservation division, solver dispatch, convergence criteria, ABI, or memory layout.

Verification

Failing before:

$ ctest --test-dir build -R '^join_failure_diagnostic_test$' --output-on-failure
ERROR STOP FAIL: join normalization output is absent
0% tests passed, 1 tests failed out of 1

Passing after:

$ ctest --test-dir build -R '^join_failure_diagnostic_test$' --output-on-failure
100% tests passed, 0 tests failed out of 1

$ fo
Static: OK (347 modules, 347 changed, 347 affected)
Build: OK
Tests: OK
Lint: OK
All stages passed (.9s)