Merge bitcoin#25773: test: Target exact weight in MiniWallet _bulk_tx

fa2537c test: Target exact weight in MiniWallet _bulk_tx (MacroFake)

Pull request description:

  Seems better to target the exact weight than a weight that is up to more than 2000 WU larger.

  Also, replace a broad `-acceptnonstdtxn=1` with `-datacarriersize=100000` to document the test assumptions better.

ACKs for top commit:
  theStack:
    Code-review ACK fa2537c

Tree-SHA512: cf02c3082a13195b8aa730866aeaf2575ce01974ae2b0244739d8cfc12e60c66312729ed703bb3214651744166a3b560bfaa8dc302ef46ed79fc4d1fe7fcc214

Author: claude

test/functional/mempool_package_limits.py

@@ -33,8 +33,8 @@ def run_test(self):
         self.test_anc_count_limits_2()
         self.test_anc_count_limits_bushy()
 
-        # The node will accept our (nonstandard) extra large OP_RETURN outputs
-        self.restart_node(0, extra_args=["-acceptnonstdtxn=1"])
+        # The node will accept (nonstandard) extra large OP_RETURN outputs
+        self.restart_node(0, extra_args=["-datacarriersize=100000"])
         self.test_anc_size_limits()
         self.test_desc_size_limits()
 

test/functional/test_framework/wallet.py

@@ -29,9 +29,10 @@
 )
 from test_framework.script import (
     CScript,
-    SignatureHash,
-    OP_TRUE,
     OP_NOP,
+    OP_RETURN,
+    OP_TRUE,
+    SignatureHash,
     SIGHASH_ALL,
 )
 from test_framework.script_util import (
@@ -97,11 +98,13 @@ def _bulk_tx(self, tx, target_weight):
         """Pad a transaction with extra outputs until it reaches a target weight (or higher).
         returns the tx
         """
-        assert_greater_than_or_equal(target_weight, tx.get_weight())
-        while tx.get_weight() < target_weight:
-            script_pubkey = ( b"6a4d0200"  # OP_RETURN OP_PUSH2 512 bytes
-                + b"01" * 512 )
-            tx.vout.append(CTxOut(0, script_pubkey))
+        tx.vout.append(CTxOut(nValue=0, scriptPubKey=CScript([OP_RETURN, b'a'])))
+        dummy_vbytes = (target_weight - tx.get_weight() + 3) // 4
+        tx.vout[-1].scriptPubKey = CScript([OP_RETURN, b'a' * dummy_vbytes])
+        # Lower bound should always be off by at most 3
+        assert_greater_than_or_equal(tx.get_weight(), target_weight)
+        # Higher bound should always be off by at most 3 + 12 weight (for encoding the length)
+        assert_greater_than_or_equal(target_weight + 15, tx.get_weight())
 
     def get_balance(self):
         return sum(u['value'] for u in self._utxos)