test, contrib: Fix signer/miner command line escaping

Pass bitcoin binary command lines from test framework to signet/miner utility
using shell escaping so they are unambigous and don't get mangled if they
contain spaces.

This change is not needed for tests to pass currently, but is a useful change
to avoid CI failures in followup PR
https://github.com/bitcoin/bitcoin/pull/31375 and to avoid other bugs.

contrib/signet/miner

@@ -9,7 +9,7 @@ import logging
 import math
 import os
 import re
-import struct
+import shlex
 import sys
 import time
 import subprocess
@@ -86,7 +86,7 @@ def finish_block(block, signet_solution, grind_cmd):
         block.solve()
     else:
         headhex = CBlockHeader.serialize(block).hex()
-        cmd = grind_cmd.split(" ") + [headhex]
+        cmd = shlex.split(grind_cmd) + [headhex]
         newheadhex = subprocess.run(cmd, stdout=subprocess.PIPE, input=b"", check=True).stdout.strip()
         newhead = from_hex(CBlockHeader(), newheadhex.decode('utf8'))
         block.nNonce = newhead.nNonce
@@ -479,7 +479,7 @@ def do_calibrate(args):
         header.nTime = i
         header.nNonce = 0
         headhex = header.serialize().hex()
-        cmd = args.grind_cmd.split(" ") + [headhex]
+        cmd = shlex.split(args.grind_cmd) + [headhex]
         newheadhex = subprocess.run(cmd, stdout=subprocess.PIPE, input=b"", check=True).stdout.strip()
 
     avg = (time.time() - start) * 1.0 / TRIALS
@@ -549,7 +549,7 @@ def main():
 
     args = parser.parse_args(sys.argv[1:])
 
-    args.bcli = lambda *a, input=b"", **kwargs: bitcoin_cli(args.cli.split(" "), list(a), input=input, **kwargs)
+    args.bcli = lambda *a, input=b"", **kwargs: bitcoin_cli(shlex.split(args.cli), list(a), input=input, **kwargs)
 
     if hasattr(args, "address") and hasattr(args, "descriptor"):
         args.derived_addresses = {}

test/functional/tool_signet_miner.py

@@ -5,6 +5,7 @@
 """Test signet miner tool"""
 
 import os.path
+import shlex
 import subprocess
 import sys
 import time
@@ -54,10 +55,10 @@ class SignetMinerTest(BitcoinTestFramework):
         subprocess.run([
                 sys.executable,
                 signet_miner_path,
-                f'--cli={" ".join(rpc_argv)}',
+                f'--cli={shlex.join(rpc_argv)}',
                 'generate',
                 f'--address={node.getnewaddress()}',
-                f'--grind-cmd={" ".join(util_argv)}',
+                f'--grind-cmd={shlex.join(util_argv)}',
                 f'--nbits={DIFF_1_N_BITS:08x}',
                 f'--set-block-time={int(time.time())}',
                 '--poolnum=99',