feat: TYPE_LABEL = "Storage" replaces storage_device = True flag

The TYPE_LABEL attribute on the base class hierarchy is now the
canonical way for drivers to declare their device category. The
storage_device sentinel flag is removed — classification is determined
by reading TYPE_LABEL via getattr() in the backend.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

napalm_openmediavault/__init__.py

@@ -14,9 +14,9 @@ Usage::
 
     driver = OpenMediaVaultDriver("192.168.1.10", "admin", "secret")
     driver.open()
-    print(driver.get_facts())
-    print(driver.get_disks())
-    print(driver.get_shares())
+    facts = driver.get_facts()
+    disks = driver.get_disks()
+    shares = driver.get_shares()
     driver.close()
 """