Find the console log handler by type when changing verbosity

set_verbose_logging() adjusted the first handler on the "mvt" logger,
whichever handler that happened to be. Anything else attaching a
handler to that logger - an embedding application, a plugin, a test
harness - had it mistaken for the console and raised or lowered behind
its back, and the same slot can hold the file handler a command
attaches to its output folder, whose level a --verbose flag should
never decide: command.log records the whole run either way.

Walk the handlers instead and adjust only MVT's own console handler,
found by its MVTLogHandler type. Every other handler on the logger is
left alone. Behaviour is otherwise unchanged.

tests/common/test_utils.py

@@ -18,6 +18,7 @@ from mvt.common.utils import (
     generate_hashes_from_path,
     get_sha256_from_file_path,
     init_logging,
+    set_verbose_logging,
 )
 
 from ..utils import get_artifact_folder
@@ -122,3 +123,29 @@ class TestInitLogging:
             sum(isinstance(handler, MVTLogHandler) for handler in log.handlers)
             == handler_count
         )
+
+    def test_verbose_logging_finds_the_console_handler_among_others(self):
+        # Something else may have attached a handler to the "mvt" logger
+        # before MVT did, so the console handler is not always the first.
+        log = logging.getLogger("mvt")
+        init_logging()
+        foreign_handler = logging.NullHandler()
+        foreign_handler.setLevel(logging.CRITICAL)
+        log.handlers.insert(0, foreign_handler)
+
+        try:
+            set_verbose_logging(True)
+            console_handlers = [
+                handler
+                for handler in log.handlers
+                if isinstance(handler, MVTLogHandler)
+            ]
+            assert console_handlers
+            assert all(handler.level == logging.DEBUG for handler in console_handlers)
+            assert foreign_handler.level == logging.CRITICAL
+
+            set_verbose_logging(False)
+            assert all(handler.level == logging.INFO for handler in console_handlers)
+            assert foreign_handler.level == logging.CRITICAL
+        finally:
+            log.handlers.remove(foreign_handler)