Merge bitcoin/bitcoin#22378: test: remove confusing MAX_BLOCK_BASE_SIZE

607076d01b test: remove confusing `MAX_BLOCK_BASE_SIZE` (Sebastian Falbesoner)
4af97c74ed test: introduce `get_weight()` helper for CBlock (Sebastian Falbesoner)
a084ebe133 test: introduce `get_weight()` helper for CTransaction (Sebastian Falbesoner)

Pull request description:

  This is a very late follow-up PR to #10618, which removed the constant `MAX_BLOCK_BASE_SIZE` from the core implementation about four years ago (see also #10608 in why it was considered confusing and superfluous).
  Since there is also no point in still keeping it in the functional test framework, the PR switches to weight-based accounting on the relevant test code parts and use `MAX_BLOCK_WEIGHT` instead for the block limit checks. To prepare that, the first two commits introduce `get_weight()` helpers for the classes CTransaction and CBlock, respectively.

ACKs for top commit:
  MarcoFalke:
    review ACK 607076d01b 🚴

Tree-SHA512: d59aa0b6b3dfd0a849b8063e66de275d252f705f99e25cd3bf6daec028b47d946777ee5b42a060f5283cb18e917ac073119c2c0e11bbc21211f69ef0a6ed335a

test/functional/mempool_accept.py

@@ -15,7 +15,7 @@ from test_framework.messages import (
     COutPoint,
     CTxIn,
     CTxOut,
-    MAX_BLOCK_BASE_SIZE,
+    MAX_BLOCK_WEIGHT,
     MAX_MONEY,
     tx_from_hex,
 )
@@ -209,7 +209,7 @@ class MempoolAcceptanceTest(BitcoinTestFramework):
 
         self.log.info('A really large transaction')
         tx = tx_from_hex(raw_tx_reference)
-        tx.vin = [tx.vin[0]] * math.ceil(MAX_BLOCK_BASE_SIZE / len(tx.vin[0].serialize()))
+        tx.vin = [tx.vin[0]] * math.ceil(MAX_BLOCK_WEIGHT // 4 / len(tx.vin[0].serialize()))
         self.check_mempool_result(
             result_expected=[{'txid': tx.rehash(), 'allowed': False, 'reject-reason': 'bad-txns-oversize'}],
             rawtxs=[tx.serialize().hex()],