test: properly check for per-tx sigops limit

Currently the per-tx sigops limit standardness check (bounded by
`MAX_STANDARD_TX_SIGOPS_COST`, throwing "bad-txns-too-many-sigops"
if exceeded) is only indirectly tested with the much higher per-block
consensus limit (`MAX_BLOCK_SIGOPS_COST`), i.e. an increase in the
limit would still pass all tests. Refine that by splitting up the invalid
tx template `TooManySigops` in a per-block and a per-tx one.

The involved functional tests taking use of these templates are
`feature_block.py` and `p2p_invalid_txs.py`.

test/functional/data/invalid_txs.py

@@ -30,7 +30,11 @@ from test_framework.messages import (
     MAX_MONEY,
     SEQUENCE_FINAL,
 )
-from test_framework.blocktools import create_tx_with_script, MAX_BLOCK_SIGOPS
+from test_framework.blocktools import (
+    create_tx_with_script,
+    MAX_BLOCK_SIGOPS,
+    MAX_STANDARD_TX_SIGOPS,
+)
 from test_framework.script import (
     CScript,
     OP_0,
@@ -233,7 +237,7 @@ class InvalidOPIFConstruction(BadTxTemplate):
             amount=(self.spend_avail // 2))
 
 
-class TooManySigops(BadTxTemplate):
+class TooManySigopsPerBlock(BadTxTemplate):
     reject_reason = "bad-txns-too-many-sigops"
     block_reject_reason = "bad-blk-sigops, out-of-bounds SigOpCount"
     expect_disconnect = False
@@ -245,6 +249,20 @@ class TooManySigops(BadTxTemplate):
             output_script=lotsa_checksigs,
             amount=1)
 
+
+class TooManySigopsPerTransaction(BadTxTemplate):
+    reject_reason = "bad-txns-too-many-sigops"
+    expect_disconnect = False
+    valid_in_block = True
+
+    def get_tx(self):
+        lotsa_checksigs = CScript([OP_CHECKSIG] * (MAX_STANDARD_TX_SIGOPS + 1))
+        return create_tx_with_script(
+            self.spend_tx, 0,
+            output_script=lotsa_checksigs,
+            amount=1)
+
+
 def getDisabledOpcodeTemplate(opcode):
     """ Creates disabled opcode tx template class"""
     def get_tx(self):

test/functional/test_framework/blocktools.py

@@ -49,6 +49,7 @@ from .util import assert_equal
 
 MAX_BLOCK_SIGOPS = 20000
 MAX_BLOCK_SIGOPS_WEIGHT = MAX_BLOCK_SIGOPS * WITNESS_SCALE_FACTOR
+MAX_STANDARD_TX_SIGOPS = 4000
 MAX_STANDARD_TX_WEIGHT = 400000
 
 # Genesis block time (regtest)