improve perf of eden clone

Summary:
improve perf of eden clone

Eden clone takes around 2 seconds, and it includes calling `hg config --local` command 2
times in row where each call takes ~300 ms. So, this diff would make the config
setup into 1 `hg config` call saving us 300 ms of time, wich is a good win for
SCM on RE project where we aim to minimise latency.

Reviewed By: muirdm

Differential Revision: D68893490

fbshipit-source-id: 19dc9beacb1ac127de1ba15fbe751541a2d0626d

eden/fs/cli/config.py

@@ -816,17 +816,18 @@ def _post_clone_checkout_setup(
                 env=env,
             )
 
-            configs = dict()
+            configs = {}
             if checkout.get_config().scm_type == "filteredhg":
                 configs["extensions.edensparse"] = ""
                 configs["extensions.sparse"] = "!"
-            for k, v in configs.items():
+            if len(configs) > 0:
+                args = [f"{k}={v}" for k, v in configs.items()]
                 subprocess.check_call(
                     [
                         os.environ.get("EDEN_HG_BINARY", "hg"),
                         "config",
                         "--local",
-                        f"{k}={v}",
+                        *args,
                         "-R",
                         str(checkout.path),
                     ],