fix: nil dereference on aggregator retries

[Oppen]

fix: nil dereference on aggregator

SendAggregatedResponse would overwrite tx, which in the error case sets it to nil, causing the retry to dereference nil.

This fix consists on using separate variables for the simulated tx and the real one.

Type of change

• [x] Bug fix

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