defaults : change type of MISC_CACHE_DIR_PATH to str

DEFAULT_MISC_CACHE_DIR_PATH was a Path but the fallbacks of config.get
in config.py will be converted to a string so make it a string instead
and do the conversion later

src/unisync/defaults.py

@@ -15,4 +15,4 @@ DEFAULT_SERVER_PORT: int = 22
 DEFAULT_ROOTS_LOCAL: str = str(Path("~/files").expanduser())
 # DEFAULT_ROOTS_REMOTE: str = ""
 
-DEFAULT_MISC_CACHE_DIR_PATH: Path = Path("~/.unisync").expanduser()
+DEFAULT_MISC_CACHE_DIR_PATH: str = "~/.unisync"