add duplicate hashes list for mainnet

[gzliudan]

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[coderabbitai]

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💤 Files selected but had no reviewable changes (1)

• docs/xdcchain/developers/duplicate-hashes-mainnet.txt

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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