tests: Skip SQLite fsyncs while testing

Since we want tests to run quickly, and since tests do a lot more db
operations than expected we expect to see in actual usage, we disable
sqlite's syncing behavior to make db operations run much faster. This
syncing behavior is necessary for normal operation as it helps guarantee
that data won't become lost or corrupted, but in tests, we don't care
about that.

test/functional/test_framework/util.py

@@ -374,6 +374,8 @@ def write_config(config_path, *, n, chain, extra_config=""):
         f.write("upnp=0\n")
         f.write("natpmp=0\n")
         f.write("shrinkdebugfile=0\n")
+        # To improve SQLite wallet performance so that the tests don't timeout, use -unsafesqlitesync
+        f.write("unsafesqlitesync=1\n")
         f.write(extra_config)