pytest: increase test_generate_coinmoves to 5M entries.

This is slow, but will make sure we find out if we add latency spikes in future.

tests/test_coinmoves.py::test_generate_coinmoves (5,000,000, sqlite3):
	Time (from start to end of l2 node):	 236 seconds
	Worst latency:				 0.15 seconds

tests/test_coinmoves.py::test_generate_coinmoves (5,000,000, Postgres):
	Time (from start to end of l2 node):	 557 seconds
	Worst latency:				 0.16 seconds

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: lightningd: multiple signficant speedups for large nodes, especially preventing "freezes" under exceptionally high load.

Author: rustyrussell

tests/test_coinmoves.py

@@ -2108,8 +2108,8 @@ def test_generate_coinmoves(node_factory, bitcoind, executor):
     next_timestamp = entries[-1]['timestamp'] + 1
 
     batch = []
-    # Let's make 2 million entries.
-    for _ in range(2_000_000 // len(entries)):
+    # Let's make 5 million entries.
+    for _ in range(5_000_000 // len(entries)):
         # Random payment_hash
         entries[0]['payment_hash'] = entries[1]['payment_hash'] = random.randbytes(32)
         entries[2]['payment_hash'] = random.randbytes(32)