avoid calling header_hash repeatedly in weight_proof (Chia-Network#4060)

header_hash is a property that serializes and hash the foliage block, this is somewhat expensive, especially the serialization

chia/full_node/weight_proof.py

@@ -395,7 +395,6 @@ async def __first_sub_slot_vdfs(
         curr = header_blocks[curr_sub_rec.header_hash]
         sub_slots_data: List[SubSlotData] = []
         tmp_sub_slots_data: List[SubSlotData] = []
-        curr = header_blocks[curr.header_hash]
         while curr.height < header_block.height:
             if curr is None:
                 log.error("failed fetching block")
@@ -457,14 +456,17 @@ async def __slot_end_vdf(
         # gets all vdfs first sub slot after challenge block to last sub slot
         log.debug(f"slot end vdf start height {start_height}")
         curr = header_blocks[self.blockchain.height_to_hash(start_height)]
+        curr_header_hash = curr.header_hash
         sub_slots_data: List[SubSlotData] = []
         tmp_sub_slots_data: List[SubSlotData] = []
-        while not blocks[curr.header_hash].is_challenge_block(self.constants):
+        while not blocks[curr_header_hash].is_challenge_block(self.constants):
             if curr.first_in_sub_slot:
                 sub_slots_data.extend(tmp_sub_slots_data)
+
+                curr_prev_header_hash = curr.prev_header_hash
                 # add collected vdfs
                 for idx, sub_slot in enumerate(curr.finished_sub_slots):
-                    prev_rec = blocks[curr.prev_header_hash]
+                    prev_rec = blocks[curr_prev_header_hash]
                     eos_vdf_iters = prev_rec.sub_slot_iters
                     if idx == 0:
                         eos_vdf_iters = uint64(prev_rec.sub_slot_iters - prev_rec.ip_iters(self.constants))
@@ -473,6 +475,8 @@ async def __slot_end_vdf(
             tmp_sub_slots_data.append(self.handle_block_vdfs(curr, blocks))
 
             curr = header_blocks[self.blockchain.height_to_hash(uint32(curr.height + 1))]
+            curr_header_hash = curr.header_hash
+
         if len(tmp_sub_slots_data) > 0:
             sub_slots_data.extend(tmp_sub_slots_data)
         log.debug(f"slot end vdf end height {curr.height} slots {len(sub_slots_data)} ")