Passing in malformed inputs as "ScopedKeys" gives raw 500 error

[hmacdope]

Passing in a malformed key to one of the API endpoints (e.g /exists/blah) causes a 500 HTTP exception to be thrown.

This is caused by attempting to unpack the malformed key to a ScopedKey, here: https://github.com/openforcefield/alchemiscale/blob/main/alchemiscale/interface/api.py#L99C40-L100C1

Where an exception should be caught if the key cannot be unpacked into its components. This is possibly a problem in other API functions also and probably needs a more general solution.