Log how long each extension module takes to import (#1171)

* Log how long each extension module takes to import

Based on some detailed debugging in
2i2c-org/infrastructure#2047
to figure out why a Jupyter Server *process* somtimes takes more than
30s
to start, the primary culprit was server extensions that took
multiple seconds to just even import. Thanks to some ad-hoc
patching (2i2c-org/infrastructure#2047 (comment)),
I was able to figure out which were the slow extensions.
This PR emits extension import time as log messages, so this
information is *much* more visible.

I also explicitly chose info instead of debug, primarily because
I believe it is *very* important to surface this performance
information to users, so they can go bug the appropriate extension.
Otherwise, it just feels like 'jupyter server is slow!'. This is
compounded by the fact that while notebook server doesn't import
*disabled* extensions, jupyter_server does seem to - so it's hard
to isolate this.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Account for the possibility logger is None

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: yuvipanda

jupyter_server/extension/utils.py

@@ -1,5 +1,6 @@
 """Extension utilities."""
 import importlib
+import time
 import warnings
 
 
@@ -62,7 +63,15 @@ def get_metadata(package_name, logger=None):
     If it doesn't exist, return a basic metadata packet given
     the module name.
     """
+    start_time = time.perf_counter()
     module = importlib.import_module(package_name)
+    end_time = time.perf_counter()
+    duration = end_time - start_time
+    # Sometimes packages can take a *while* to import, so we report how long
+    # each module took to import. This makes it much easier for users to report
+    # slow loading modules upstream, as slow loading modules will block server startup
+    if logger:
+        logger.info(f"Package {package_name} took {duration:.4f}s to import")
 
     try:
         return module, module._jupyter_server_extension_points()