feat(aggregation): score interval-2 jobs like the block builder

The interval-2 session aggregated current-slot gossip groups in arbitrary
order and ignored existing proofs, so it could not prioritize the groups
whose aggregation most advances consensus. Rework snapshot_aggregation_inputs
into a tiered greedy selector modeled on select_attestations: an up-front
store pass resolves each candidate's material once (raw-first + trim), then a
loop scores candidates by (current-slot-first, Finalize > Justify > Build)
against an optimistically-projected state, emitting at most
MAX_AGGREGATION_JOBS jobs.

Candidates are filtered by the block builder's entry_passes_filters against a
chain view covering [0, head_slot] (head root pushed onto the state's
historical_block_hashes, which omits the head's own root), so prover time is
spent only on aggregations a block could actually pack.

Reuses the block builder's shared, coverage-based score_entry, its
ProjectedState (from_head_state + advance), and entry_passes_filters, so
proposer and aggregator can never drift on either the justify/finalize
projection or the tiering. The aggregator passes each job's realized
raw + child coverage straight to score_entry. Deletes
snapshot_current_slot_aggregation_inputs and build_raw_signature_job
(subsumed).

Builds on the block_builder refactor (shared ProjectedState + coverage-based
score_entry).

Author: MegaRedHand

Cargo.lock

@@ -40,6 +40,8 @@ hex = { workspace = true }
 libssz.workspace = true
 libssz-types.workspace = true
 datatest-stable = "0.3.3"
+leansig.workspace = true
+rand.workspace = true
 
 [[test]]
 name = "forkchoice_spectests"