Record the source of loaded modules for auditability

Now that installed module packages load automatically, record where every
module came from:

- --list-modules groups the available modules by source, one line per
  source with the modules comma-separated: MVT itself with its version,
  each installed package with its version and VCS commit when recorded
  (PEP 610 direct_url.json), and each --load-module/MVT_CUSTOM_MODULES
  file with its SHA-256 hash.
- Commands log one line per module source with its version or hash and
  the modules loaded from it, so command.log records exactly which
  modules ran and where they came from.
- Make init_logging() idempotent: a loaded module package importing an
  MVT CLI module would previously add a second console handler and
  duplicate every console log line.

tests/common/test_utils.py

@@ -8,6 +8,7 @@ import logging
 import os
 from datetime import datetime
 
+from mvt.common.log import MVTLogHandler
 from mvt.common.utils import (
     CustomJSONEncoder,
     convert_datetime_to_iso,
@@ -16,6 +17,7 @@ from mvt.common.utils import (
     convert_unix_to_utc_datetime,
     generate_hashes_from_path,
     get_sha256_from_file_path,
+    init_logging,
 )
 
 from ..utils import get_artifact_folder
@@ -103,3 +105,20 @@ class TestCustomJSONEncoder:
             json.dumps({"name": "家".encode()}, cls=CustomJSONEncoder)
             == '{"name": "\\u5bb6"}'
         )
+
+
+class TestInitLogging:
+    def test__init_logging_is_idempotent(self):
+        # Loaded module packages may import an MVT CLI module, which calls
+        # init_logging() again at import time. A second call must not add
+        # a duplicate console handler.
+        log = logging.getLogger("mvt")
+        init_logging()
+        handler_count = sum(
+            isinstance(handler, MVTLogHandler) for handler in log.handlers
+        )
+        init_logging()
+        assert (
+            sum(isinstance(handler, MVTLogHandler) for handler in log.handlers)
+            == handler_count
+        )