mining: reject invalid block create options

Check BlockCreateOptions before block template creation instead of
clamping runtime values. This makes invalid runtime block creation
options, including those passed by IPC mining clients, fail explicitly
instead of silently mining with different values than the caller
requested.

Runtime option validation now uses the same error wording as startup
option validation. Startup validation also rejects -blockmaxweight
values lower than -blockreservedweight instead of allowing them to be
clamped later.

Co-authored-by: Ryan Ofsky <ryan@ofsky.org>

test/functional/mining_basic.py

@@ -374,6 +374,13 @@ class MiningTest(BitcoinTestFramework):
             expected_msg=f"Error: -blockmaxweight ({MAX_BLOCK_WEIGHT + 1}) exceeds consensus maximum block weight ({MAX_BLOCK_WEIGHT})",
         )
 
+        self.log.info("Test that node will fail to start when -blockmaxweight is lower than -blockreservedweight")
+        self.stop_node(0)
+        self.nodes[0].assert_start_raises_init_error(
+            extra_args=[f"-blockmaxweight={DEFAULT_BLOCK_RESERVED_WEIGHT - 1}"],
+            expected_msg=f"Error: -blockreservedweight ({DEFAULT_BLOCK_RESERVED_WEIGHT}) exceeds -blockmaxweight ({DEFAULT_BLOCK_RESERVED_WEIGHT - 1})",
+        )
+
     def test_height_in_locktime(self):
         self.log.info("Sanity check generated blocks have their coinbase timelocked to their height.")
         self.generate(self.nodes[0], 1, sync_fun=self.no_op)