bleak: include %(threadName)s in BLEAK_LOGGING (#1144)

This adds `%(threadName)s` to `FORMAT` passed to `logging.basicConfig()`
when `BLEAK_LOGGING` is used. This can be useful to debug OS callbacks
on background threads.

CHANGELOG.rst

@@ -22,6 +22,7 @@ Changed
 * ``BLEDevice`` now uses ``__slots__`` to reduce memory usage.
 * ``BaseBleakClient.services`` is now ``None`` instead of empty service collection
   until services are discovered.
+* Include thread name in ``BLEAK_LOGGING`` output. Merged #1144.
 
 Fixed
 -----

bleak/__init__.py

@@ -60,7 +60,7 @@
 _logger = logging.getLogger(__name__)
 _logger.addHandler(logging.NullHandler())
 if bool(os.environ.get("BLEAK_LOGGING", False)):
-    FORMAT = "%(asctime)-15s %(name)-8s %(levelname)s: %(message)s"
+    FORMAT = "%(asctime)-15s %(name)-8s %(threadName)s %(levelname)s: %(message)s"
     handler = logging.StreamHandler(sys.stdout)
     handler.setLevel(logging.DEBUG)
     handler.setFormatter(logging.Formatter(fmt=FORMAT))