Consensus: Ensure validators are not read from uncle blocks

[SuperFluffy]

Describe the feature

When reading validators from the on-chain contract, only the block number is considered. In very rare cases, this opens us up to reading uncle blocks instead of the intended canonical block if a) the excecution layer has previously canonicalized some other block for the target height, and b) the DKG actor reads the block before the application actor gets to finalize the block. We should read digest of the block instead.

https://github.com/tempoxyz/tempo/blob/5de51f39e176f22b9dcf32b11eeaf5eb312a468a/crates/commonware-node/src/dkg/manager/validators.rs#L43

Additional context

No response