fix(pruning): memory leak pruning tx indexer iterator

[srene]

PR Standards

Opening a pull request should be able to meet the following requirements

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PR naming convention: https://hackmd.io/@nZpxHZ0CT7O5ngTp0TP9mg/HJP_jrm7A

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Close #1145

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For Author:

• Targeted PR against correct branch
• included the correct type prefix in the PR title
• Linked to Github issue with discussion and accepted design
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• Wrote unit and integration tests
• All CI checks have passed
• Added relevant godoc comments

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For Reviewer:

• confirmed the correct type prefix in the PR title
• Reviewers assigned
• confirmed all author checklist items have been addressed

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After reviewer approval:

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