chore(number-field-mathlib): re-audit phase evidence

[kim-em]

Summary

• audit the complete HexNumberFieldMathlib public surface and confirm the explicit correspondence-only classification
• map transported operations to the five Mathlib-free conformance/performance owners
• record the absence of dedicated conformance, benchmark, report, and proof-probe artifacts
• re-attest Phases 3–4 and preserve the valid later-phase record

Verification

• lake build HexNumberFieldMathlib HexNumberField.Conformance HexRoots.Conformance HexResultant.Conformance HexBerlekampZassenhaus.Conformance HexPolyZ.Conformance
• lake build (10,500 jobs)
• python3 -m unittest scripts/test_check_dag.py
• python3 scripts/check_dag.py
• python3 scripts/check_phase4.py
• python3 scripts/check_phase7.py
• conformance-target, release-manifest, manual-split, trust-surface, copyright, file-line-count, and diff checks

Closes #9666