Add gRPC CProvider impl

[corverroos]

Problem to Solve

CProvider currently uses the CometBFT RPC to query CosmosSDK application state (attest/portal/valsync modules).

CometBFT however implements a sequential concurrency model. So queries and block processing compete for time resources. See cosmos/cosmos-sdk#10859.

Queries are therefore slower, and high query load can negatively affect block building latency. See #1865 .

Local simnet testing showed that gRPC is 2x~3x faster than CometBFT.

Proposed Solution

• Add a second gRPC based CProvider implementation.
• Note we'll need to remove the CometClient method (only used by xconnector).
• We don't expose gRPC API publicly on staging or omega yet, so all external use still need to use the CometBFT impl.
• First usage of gRPC could be validators querying themselves.
• Second could be relayer querying archive nodes (ensure firewall is open)
• Third, think about and discuss exposing the gRPC API publicly (and create subsequent ticket).