refactor: simplify signature timeout logic

[Oppen]

ProcessNewSignature already takes a context to handle cancellation and
timeout. We need just to create the context and pass it off, and it will
return an appropriate error if the timeout expires.

This saves us from creating a goroutine and handling messages just for
that.

Also improve a little bit of the error reporting.

Type of change

• Refactor

Checklist

• “Hotfix” to testnet, everything else to staging
• Linked to Github Issue
• This change depends on code or research by an external entity
  • Acknowledgements were updated to give credit
• Unit tests added
• This change requires new documentation.
  • Documentation has been added/updated.
• This change is an Optimization
  • Benchmarks added/run
• Has a known issue
  • Link to the open issue addressing it
• If your PR changes the Operator compatibility (Ex: Upgrade prover versions)
  • This PR adds compatibility for operator for both versions and do not change batcher/docs/examples
  • This PR updates batcher and docs/examples to the newer version. This requires the operator are already updated to be compatible

Testing

Basic testing: start a devnet, show it's able to verify proofs.
Alightly more involved testing: register three operators and leave only one up,
so it doesn't reach quorum, the timeout should kick.

[JuArce]

This PR is wrong. Eigen's BLSAgg service only honors the context if it can start servicing the request