test: switch MiniWallet padding unit from weight to vsize

The weight unit is merely a consensus rule detail and is largely
irrelevant for fee-rate calculations and mempool policy rules (e.g. for
package relay and TRUC limits), so there doesn't seem to be any value of
using a granularity that we can't even guarantee to reach exactly
anyway.

Switch to the more natural unit of vsize instead, which simplifies both
the padding implementation and the current tests that take use of this
padding. The rather annoying multiplications by `WITNESS_SCALE_FACTOR`
can then be removed and weird-looking magic numbers like `4004` can be
replaced by numbers that are more connected to actual policy limit
constants from the codebase, e.g. `1001` for exceeding
`TRUC_CHILD_MAX_VSIZE` by one.

test/functional/feature_framework_miniwallet.py

@@ -9,7 +9,7 @@ import string
 from test_framework.blocktools import COINBASE_MATURITY
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
-    assert_greater_than_or_equal,
+    assert_equal,
 )
 from test_framework.wallet import (
     MiniWallet,
@@ -22,17 +22,15 @@ class FeatureFrameworkMiniWalletTest(BitcoinTestFramework):
         self.num_nodes = 1
 
     def test_tx_padding(self):
-        """Verify that MiniWallet's transaction padding (`target_weight` parameter)
-           works accurately enough (i.e. at most 3 WUs higher) with all modes."""
+        """Verify that MiniWallet's transaction padding (`target_vsize` parameter)
+           works accurately with all modes."""
         for mode_name, wallet in self.wallets:
             self.log.info(f"Test tx padding with MiniWallet mode {mode_name}...")
             utxo = wallet.get_utxo(mark_as_spent=False)
-            for target_weight in [1000, 2000, 5000, 10000, 20000, 50000, 100000, 200000, 4000000,
-                                  989,  2001, 4337, 13371, 23219, 49153, 102035, 223419, 3999989]:
-                tx = wallet.create_self_transfer(utxo_to_spend=utxo, target_weight=target_weight)["tx"]
-                self.log.debug(f"-> target weight: {target_weight}, actual weight: {tx.get_weight()}")
-                assert_greater_than_or_equal(tx.get_weight(), target_weight)
-                assert_greater_than_or_equal(target_weight + 3, tx.get_weight())
+            for target_vsize in [250, 500, 1250, 2500, 5000, 12500, 25000, 50000, 1000000,
+                                 248, 501, 1085, 3343, 5805, 12289, 25509, 55855,  999998]:
+                tx = wallet.create_self_transfer(utxo_to_spend=utxo, target_vsize=target_vsize)["tx"]
+                assert_equal(tx.get_vsize(), target_vsize)
 
     def test_wallet_tagging(self):
         """Verify that tagged wallet instances are able to send funds."""