Move prefetcher execution as early as possible

[kjhman21]

Proposed changes

• Prefetching should be executed as early as possible.
• This commit moves the prefetch trigger to the top of the for loop without changing code semantics.
• We found that it shows little bit performance improvement. See below snapshot from grafana. (from block number 51786905)

Types of changes

Please put an x in the boxes related to your change.

• Bugfix
• New feature or enhancement
• Others

Checklist

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• I have read the CONTRIBUTING GUIDELINES doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes ($ make test)
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Related issues

• Fix the prefech logic for multiple txs of the same sender in a block #911
• Enable tx prefetcher for multiple blocks #916

[ehnuje]

LGTM, thanks!