If Geth is engaged in a long-run block synchronization, such as a full
syncing over a large number of blocks, invoking `debug_setHead` will
cause `downloader.Cancel` to wait for all fetchers to stop first.
This can be time-consuming, particularly for the block processing
thread.
To address this, we manually call `blockchain.StopInsert` to interrupt
the blocking processing thread and allow it to exit immediately, and
after that call `blockchain.ResumeInsert` to resume the block
downloading process.
Additionally, we add a sanity check for the input block number of
`debug_setHead` to ensure its validity.
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Signed-off-by: jsvisa <delweng@gmail.com>
Co-authored-by: Gary Rong <garyrong0905@gmail.com>
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