fix: close the Client's aio session if the websocket fails to connect

[tconbeer]

closes #49

Another option is to fix this in Textual itself; you can remove the guard here:

https://github.com/Textualize/textual/blob/3427dbaed666a9af926c711c0eed552260738cd2/src/textual/app.py#L3605-L3606

and just call self._disconnect_devtools(), since that checks for the presence of devtools (but doesn't check if it's connected).

A third option is to call self_disconnect_devtools() when handling the exception raised by the connection failure:

https://github.com/Textualize/textual/blob/3427dbaed666a9af926c711c0eed552260738cd2/src/textual/app.py#L3212-L3213