account overrides: parse hex string into nonce long

[macfarla]

PR description

Fixed Issue(s)

fixes #7998

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• Considered documentation and added the doc-change-required label to this PR if updates are required.
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• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

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

[Gabriel-Trintinalia]

lgtm