Devnet4: dual-key validators, block signing, and type migration (#233) (incl. #275 #277)

## Motivation

Implements devnet4
([leanSpec#449](leanEthereum/leanSpec#449)):
separate attestation and proposal keys for validators, replacing the
single-key model and removing the proposer attestation wrapper.

## Description

### Phase 1: Types (#230)
- `Validator` gains `attestation_pubkey` + `proposal_pubkey` (replaces
single `pubkey`)
- `SignedBlockWithAttestation` → `SignedBlock`, `BlockWithAttestation`
deleted
- Genesis config updated to dual-key YAML format

### Phase 2: Key manager + block proposal (#231)
- `ValidatorKeyPair` with separate attestation/proposal secret keys
- Block proposal signs `hash_tree_root(block)` with proposal key (no
proposer attestation)
- All validators now attest at interval 1 (proposer no longer skipped)

### Phase 3: Store + verification (#232)
- Signature verification uses `get_attestation_pubkey()` /
`get_proposal_pubkey()` as appropriate
- Removed ~40 lines of proposer attestation handling from
`on_block_core`
- Storage reads/writes `SignedBlock` directly

### Phase 4: Network + tests (#233)
- Type rename cascade across all network layer files
- Test harness updated: removed `ProposerAttestation`, simplified
`build_signed_block()`
- Added proposal signing metrics
- leanSpec bumped to 9c30436 (dual-key test fixtures)
- Skipped `test_reorg_with_slot_gaps` (fixture relies on gossip proposer
attestation state)

## Supersedes
Closes #230, closes #231, closes #232

## Blockers
- **lean-quickstart**: needs devnet4 genesis config support for manual
devnet testing

---------

Co-authored-by: Tomás Grüner <47506558+MegaRedHand@users.noreply.github.com>

Author: pablodeymo

.claude/skills/devnet-log-review/references/CLIENT_LOG_PATTERNS.md

@@ -54,7 +54,6 @@ ethlambda_p2p: Published block to gossipsub slot=X proposer=Y
 ```
 ethlambda_blockchain: Published attestation slot=X validator_id=Y
 ethlambda_p2p::gossipsub::handler: Received new attestation from gossipsub, sending for processing slot=X validator=Y
-ethlambda_blockchain: Skipping attestation for proposer slot=X (expected: proposers don't attest to their own slot)
 ```
 
 ### Block Processing

CLAUDE.md

@@ -48,7 +48,7 @@ crates/
 ### Tick-Based Validator Duties (4-second slots, 5 intervals per slot)
 ```
 Interval 0: Block proposal → accept attestations if proposal exists
-Interval 1: Vote propagation (no action)
+Interval 1: Attestation production (all validators, including proposer)
 Interval 2: Aggregation (aggregators create proofs from gossip signatures)
 Interval 3: Safe target update (fork choice)
 Interval 4: Accept accumulated attestations
@@ -106,7 +106,7 @@ let byte: u8 = code.into();
 ### Ownership for Large Structures
 ```rust
 // Prefer taking ownership to avoid cloning large data (signatures ~3KB)
-pub fn insert_signed_block(&mut self, root: H256, signed_block: SignedBlockWithAttestation) { ... }
+pub fn insert_signed_block(&mut self, root: H256, signed_block: SignedBlock) { ... }
 
 // Add .clone() at call site if needed - makes cost explicit
 store.insert_signed_block(block_root, signed_block.clone());
@@ -310,8 +310,8 @@ Both servers are spawned as independent `tokio::spawn` tasks from `main.rs`. Bin
 ```yaml
 GENESIS_TIME: 1770407233
 GENESIS_VALIDATORS:
-  - "cd323f232b34ab26d6db7402c886e74ca81cfd3a..."  # 52-byte XMSS pubkeys (hex)
-  - "b7b0f72e24801b02bda64073cb4de6699a416b37..."
+  - attestation_pubkey: "cd323f232b34ab26d6db7402c886e74ca81cfd3a..."  # 52-byte XMSS pubkeys (hex)
+    proposal_pubkey: "b7b0f72e24801b02bda64073cb4de6699a416b37..."
 ```
 - Validator indices are assigned sequentially (0, 1, 2, ...) based on array order
 - All genesis state fields (checkpoints, justified_slots, etc.) initialize to zero/empty defaults
@@ -363,7 +363,7 @@ cargo test -p ethlambda-blockchain --test forkchoice_spectests -- --test-threads
 |-------|-------------|---------|
 | `BlockHeaders` | H256 → BlockHeader | Block headers by root |
 | `BlockBodies` | H256 → BlockBody | Block bodies (empty for genesis) |
-| `BlockSignatures` | H256 → BlockSignaturesWithAttestation | Signatures (absent for genesis) |
+| `BlockSignatures` | H256 → BlockSignatures | Signatures (absent for genesis) |
 | `States` | H256 → State | Beacon states by root |
 | `LatestKnownAttestations` | u64 → AttestationData | Fork-choice-active attestations |
 | `LatestNewAttestations` | u64 → AttestationData | Pending (pre-promotion) attestations |