BlockResults Pruning

[julienrbrt]

Since #142, block results are stored each blocks to the rollkit db.
This will grow to infinity, so a pruning strategy must be introduced.

Two options were mentioned in our call:

• query x/network module for latest validated epoch, prune everything before that
• when x/network and the validator network isn't used (query fails), use a good value.
• Some food for thoughts, looking at the cometbft v1+ pruning service: https://github.com/cometbft/cometbft/blob/e1a860489ecc91290453487e08863a037f828c6d/rpc/grpc/server/services/pruningservice/service.go#L141

Given the blocks results are saved in the rollkit db, we must be sure that it doesn't overlap with evstack/ev-node#2093.

[julienrbrt]

Implemented via #332