Use runtime checks in Wycheproof client

[fegge]

Summary

• Replace verdict-bearing Wycheproof client assert statements with runtime checks.
• Ensure invalid, valid, and unsupported-result cases still fail when Python optimization disables assertions.

Validation

• ruff format test/wycheproof/wycheproof_client.py: passed
• ruff check test/wycheproof/wycheproof_client.py: passed
• python3 -m py_compile test/wycheproof/wycheproof_client.py: passed
• git diff --check -- test/wycheproof/wycheproof_client.py: passed
• rg -n '\bassert\b' test/wycheproof/wycheproof_client.py: no matches
• make wycheproof -j4: passed
• python3 test/wycheproof/wycheproof_client.py --data-dir <fresh-temp-dir>: passed
• PYTHONOPTIMIZE=1 python3 test/wycheproof/wycheproof_client.py --data-dir <fresh-temp-dir>: passed
• Tampered signing vector under PYTHONOPTIMIZE=1: failed as expected with signature mismatch tcId=1
• Not run: ./scripts/format because nixpkgs-fmt is not installed in this local environment
• Not run: ./scripts/lint because shfmt is not installed in this local environment

Fixes #1218

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This work was completed by Trail of Bits as part of the Patch The Planet project in collaboration with OpenAI. The issue was identified primarily by the Codex coding agent, and manually reviewed before submission.

[fegge]

Reopened from an upstream repository branch with DCO-signed commits so full CI can run: #1234