trie: fix two issues in trie iterator #24539

[gzliudan]

Proposed changes

This PR fixes two issues in iterator:

• Fix the memory leak in iterator.
  In trie iterator each resolved trie node will be wrapped with a struct and the corresponding pointer will be saved in the stack based slice. Whenever the node is visited, the struct is poped from stack. However this struct point should be explicitly set to nil in order to garbage collect the underlying struct.

• Fix the empty trie iterator
  The empty trie shouldn't be iterated out any values.

Ref: ethereum#24539

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)
• Regular KTLO or any of the maintaince work. e.g code style
• CICD Improvement

Impacted Components

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• Consensus
• Account
• Network
• Geth
• Smart Contract
• External components
• Not sure (Please specify below)

Checklist

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• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
• Provide an end-to-end test plan in the PR description on how to manually test it on the devnet/testnet.
• Tested the backwards compatibility.
• Tested with XDC nodes running this version co-exist with those running the previous version.
• Relevant documentation has been updated as part of this PR
• N/A