Small optimization on eth_sendRawTransaction

[ahamlat]

PR description

This PR is a small improvement on eth_sendRawTransaction, as it notifies the listeners on added transactions asynchronously. The PR also pre-calculates the sender of the transaction which is more a mitigation of the synchronized on LayeredPendingTransactions.addTransaction, the sender can be calculated by one the thread of ForkjoinPool.commonPool while the main thread is locking on syncronized.

Fixed Issue(s)

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• [x] Checked out our contribution guidelines?
• [x] Considered documentation and added the doc-change-required label to this PR if updates are required.
• [x] Considered the changelog and included an update if required.
• [x] For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• [ ] unit tests: ./gradlew build
• [ ] acceptance tests: ./gradlew acceptanceTest
• [ ] integration tests: ./gradlew integrationTest
• [ ] reference tests: ./gradlew ethereum:referenceTests:referenceTests