Function grin_chain::txhashset::sync_extending

pub fn sync_extending<'a, F, T>(
    trees: &'a mut TxHashSet, 
    batch: &'a mut Batch, 
    inner: F
) -> Result<T, Error> where
    F: FnOnce(&mut HeaderExtension) -> Result<T, Error>, 

Start a new sync MMR unit of work. This MMR tracks the sync_head. This is used during header sync to validate batches of headers as they arrive without needing to repeatedly rewind the header MMR that continues to track the header_head as they diverge during sync.