refactor(testing): type proof_setting as an IntEnum and fix its derivation

[tcoratger]

Motivation

The emitted proof_setting field was a bare int with three magic values, documented only by a re-explaining inline comment block at the single place it was assigned:

# - 0 mocked,
# - 1 real and must verify,
# - 2 real and must fail verification.
if mock_prover:
    proof_setting = 0
elif test_spec.expected_rejection is not None:
    proof_setting = 2
else:
    proof_setting = 1

Two problems:

1. Stringly/numerically typed — the meaning lives in a comment, not the type.
2. Derivation bug — proof_setting was set to 2 ("real proof must fail verification") for any vector carrying an expected rejection, even when the rejection is non-crypto (e.g. an unknown parent, a slot mismatch) and the proof is perfectly valid. A client that verifies such a proof (and it passes) then rejects for the real reason is behaving correctly, yet contradicts proof_setting=2.

What this does

Self-documenting IntEnum. Each member carries its own meaning:

class ProofSetting(IntEnum):
    MOCKED = 0           # the proof is mocked and must not be verified
    REAL_AND_VALID = 1   # the proof is real and must verify
    REAL_AND_INVALID = 2 # the proof is real and must fail verification

The fixture field is retyped to ProofSetting. Because it is an IntEnum, it serializes to the same integer (0/1/2) — emitted vectors are byte-identical — and ProofSetting.MOCKED == 0 still holds for any consumer comparing against integers.

Fixed derivation. REAL_AND_INVALID is now reserved for rejections whose direct cause is the proof failing verification:

PROOF_FAILURE_REJECTION_REASONS = frozenset(
    {RejectionReason.INVALID_SIGNATURE, RejectionReason.INVALID_BLOCK_PROOF}
)

Every other rejection keeps its valid proof and maps to REAL_AND_VALID.

The default mocked lane is unaffected (every vector is MOCKED), so generated vectors do not churn; only the real-crypto authoritative set is corrected for non-crypto negative vectors.

Testing

• just check passes (lint, format, ty, codespell, mdformat).
• Verified the field serializes to a plain int (0/1/2) for every member, and ProofSetting.MOCKED == 0.
• Verified the reason mapping: UNKNOWN_PARENT_BLOCK is not a proof failure; INVALID_SIGNATURE/INVALID_BLOCK_PROOF are.
• Mocked fill smoke on a rejection test runs clean and emits proofSetting: 0.

🤖 Generated with Claude Code