chore: replace polling with subscription-based acceptance

[RodrigoVillar]

Why this should be merged

As mentioned in #3996 (comment), we should not be polling API nodes for a transaction's status in the context of load testing. This PR modifies the awaitTx() to use block-subscriptions instead of excessive polling for determining a transaction's status.

How this works

For each block awaitTx() hears about, awaitTx() queries the nonce of the sender at the given height to determine if the sender's nonce has incremented by one (i.e. if the sender's outstanding transaction was included in a block). If the nonce has incremented, awaitTx() then makes a single call to client.TransactionReceipt() to determine if the transaction successfully executed or not.

How this was tested

CI

Need to be documented in RELEASES.md?

N/A

[Copilot]

Pull Request Overview

This PR replaces polling-based transaction confirmation with a subscription to new blocks and nonce inspection.

• Introduces a block subscription in Wallet.SendTx and refactors awaitTx to listen for headers.
• Removes pingFrequency and related polling logic.
• Updates tests to drop the PollFrequency field and adjust calls accordingly.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tests/load2/wallet.go	Adds block‐subscription logic, refactors awaitTx.
tests/load2/tests.go	Removes PollFrequency field and argument.
tests/load2/main/main.go	Updates instantiation of ZeroTransferTest.

Comments suppressed due to low confidence (1)

tests/load2/wallet.go:119

• [nitpick] Consider including the transaction hash or more context in this error (e.g., the txHash) to make failures easier to debug.

					return fmt.Errorf("failed tx: %d", receipt.Status)