feat: Store Replica Mode

[sergerad]

Store Replica Mode

Adds a replica mode to the store, enabling (replica) store instances to sync blocks and proofs
from an upstream store. This allows the RPC layer to be scaled horizontally by pointing multiple
RPC nodes at multiple replica stores, without adding load to the primary store or block producer.

Architecture

The store now operates in one of two mutually exclusive modes, controlled by the new StoreMode
enum:

• BlockProducer mode — existing behaviour. Accepts blocks from the block producer via the
  BlockProducer gRPC service, runs the proof scheduler, and exposes the NtxBuilder service.
• Replica mode — new. Syncs blocks from an upstream store via the new StoreReplica gRPC
  service. Only exposes the Rpc and StoreReplica services — no block producer service, no NTX builder service, and no proof scheduler task.

New: StoreReplica gRPC service

Implemented on the upstream store side. Exposes two streaming RPCs:

• SubscribeBlocks — streams committed blocks to a subscriber starting from a given block
  number.
• SubscribeProofs — streams block proofs to a subscriber starting from a given block number.

Operational

• run-node.sh updated to demonstrate a topology with a primary store
  and two replicas, with RPC nodes pointing at the replicas.

 # Second replica (upstream = first replica)
➜ grpcurl -plaintext -proto  ./rpc.proto -d '{}' "localhost:57293" rpc.Api/Status
{
...
  "store": {
    "version": "0.15.0",
    "status": "connected",
    "chainTip": 13
  },
...
}

# First replica (upstream = block producer store)
➜ grpcurl -plaintext -proto  ./rpc.proto -d '{}' "localhost:57292" rpc.Api/Status
{
...
  "store": {
    "version": "0.15.0",
    "status": "connected",
    "chainTip": 13
  },
...
}

[Mirko-von-Leipzig]

I'm about halfway through, I think so far my main question/suggestion is moving the proof inputs out of the db.