feat(aggregation): score interval-2 jobs like the block builder (#526)

## What

Rework `snapshot_aggregation_inputs` into a tiered greedy selector
modeled on
the block builder's `select_attestations`: an up-front store pass
resolves each
candidate's aggregation 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.

## Why

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.

## How

- Candidates are filtered by the block builder's `entry_passes_filters`
against a
chain view covering `[0, head_slot]` (the head root is 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 shared `ProjectedState` (`from_head_state` + `advance`) and
  `Tier`/`EntryScore`/`entry_passes_filters` via a coverage-based
`score_from_coverage` core, so proposer and aggregator can never drift
on
  either the justify/finalize projection or the tiering.
- Deletes `snapshot_current_slot_aggregation_inputs` and
  `build_raw_signature_job` (subsumed).

## Stacking

Stacked on #525 (the block builder refactor). Review/merge that first;
GitHub
retargets this PR to `main` once it lands.

## Checks

- `cargo fmt` clean
- `cargo clippy --all-targets -- -D warnings` clean
- `cargo test -p ethlambda-blockchain --lib` green (incl. resolve_job /
pick_best_candidate / snapshot tests)

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"