refactor(conductor): fetch missing blocks as necessary

[SuperFluffy]

Summary

Conductor fetches blocks from the rollup node if they are not in its cache.

Background

During initialization and when set to firm-and-soft commitment mode, Conductor issued a BatchGetBlocks RPC to the rollup. When the delta between firm and soft commitments was too large, this could be a request for 50k and more elements, putting a lot of pressure on the rollup node or failing outright because the request exceeded the default 4MB limit for gRPC requests.

This patch replaces this pre-fetch in favor of an already existing fallback logic: if conductor finds a Celestia block with the next desired firm-number, it either looks up the corresponding rollup block in its cache, or requests it from the rollup. It then updates the rollup's commitment state.

Changes

• Remove BatchGetBlocks logic from conductor

Testing

Update the conductor test for fetching missing rollup blocks.