refactor(testing): replace the stringly-typed signature tamper with a typed union (leanEthereum#859)

The signed-block tamper hook was a dict of magic operation strings
dispatched through a 130-line if ladder, while the proof fixtures
already model tampers as a typed union matched with structural
patterns. Migrate the laggard to the same pattern:

- one Pydantic model per mutation, each documenting the rejection
  path it exercises,
- a closed union replacing the raw dict, so a misspelled operation
  or missing argument fails at construction instead of at fill time,
- structural pattern matching replacing the if ladder.

Fixture JSON is unchanged: the tamper field is excluded from output.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: tcoratger

packages/testing/src/consensus_testing/__init__.py

@@ -6,18 +6,24 @@
 from consensus_testing.genesis import build_anchor, generate_pre_state
 from consensus_testing.test_fixtures import (
     ApiEndpointTest,
+    AppendPhantomAttestation,
     BaseConsensusFixture,
+    ClearFirstAttestationBits,
+    CorruptProof,
     DropMessageBinding,
     ForkChoiceTest,
     GossipsubHandlerTest,
     IncrementEmittedSlot,
     JustifiabilityTest,
+    MutateStateRoot,
     NetworkingCodecTest,
     PoseidonPermutationTest,
     RebindToAlternateHeadRoot,
+    SetProposerIndex,
     SlotClockTest,
     SSZTest,
     StateTransitionTest,
+    SwapFirstTwoAttestations,
     SwapMessageBindings,
     SwapParticipantPublicKey,
     SyncTest,
@@ -76,6 +82,12 @@
     "SwapMessageBindings",
     "DropMessageBinding",
     "VerifySignaturesTest",
+    "SetProposerIndex",
+    "ClearFirstAttestationBits",
+    "CorruptProof",
+    "AppendPhantomAttestation",
+    "MutateStateRoot",
+    "SwapFirstTwoAttestations",
     "SSZTest",
     "NetworkingCodecTest",
     "GossipsubHandlerTest",

packages/testing/src/consensus_testing/test_fixtures/__init__.py

@@ -20,7 +20,15 @@
     VerifyMultiMessageProofsTest,
     VerifySingleMessageProofsTest,
 )
-from consensus_testing.test_fixtures.verify_signatures import VerifySignaturesTest
+from consensus_testing.test_fixtures.verify_signatures import (
+    AppendPhantomAttestation,
+    ClearFirstAttestationBits,
+    CorruptProof,
+    MutateStateRoot,
+    SetProposerIndex,
+    SwapFirstTwoAttestations,
+    VerifySignaturesTest,
+)
 
 __all__ = [
     "BaseConsensusFixture",
@@ -34,6 +42,12 @@
     "SwapMessageBindings",
     "DropMessageBinding",
     "VerifySignaturesTest",
+    "SetProposerIndex",
+    "ClearFirstAttestationBits",
+    "CorruptProof",
+    "AppendPhantomAttestation",
+    "MutateStateRoot",
+    "SwapFirstTwoAttestations",
     "SSZTest",
     "NetworkingCodecTest",
     "GossipsubHandlerTest",