DB get_compact_block_stream slow init time with very large block ranges.

[idky137]

Currently the get_compact_block_stream in DbV1 uses validate_block_range, checking that all heights in the range hold valid data.

Currently DbV1 does run this check on startup, once heights marked as valid this is a very efficient check:

fn is_validated(&self, h: u32) -> bool {
        let tip = self.validated_tip.load(Ordering::Acquire);
        h <= tip || self.validated_set.contains(&h)
    }

However, if get_compact_block_stream is called before the initial block scan has completed, then validate_block_range will call validate_block_blocking for every height not yet in the DB's validated set or above validated tip. This can be very slow for large un-validated block ranges and currently stops get_compact_block_stream returning any blocks until complete.

This should be updated to call validate_block_blocking for each height separately, so that get_compact_block_stream does not stall for long periods, just has slightly slower performance when working with un-validated database heights.