Raise error for enum creation from invalid string values

[parthosa]

Fixes #887: This PR updates the fromstring() method for Enum creation to raise a ValueError for invalid input strings. Previously, it would silently returned None, which could lead to unexpected behaviour if not handled by the caller.

Changes

class EnumeratedType:

• fromstring() now raises a ValueError for invalid strings.
• Changed fromstring() return type to EnumeratedType.
• Added get_default() to return a default value. This is implemented by the subclasses.

[cindyyuanjiang]

Is this behavior the same? Previously, this block does not raise exception even if arg_val is not QualFilterApp, but after this changes, it could.

[parthosa]

This check seemed redundant to me. QualFilterApp argument is provided by the user, and our argument validator (argprocessor) would validates these inputs as first step. If there are invalid values, we will terminate early.

[amahussein]

This code was initially there because we had the legacy CLI that was not doing the same initialization as spark_rapids.
There pros-cons removing it:

• pros: it is redundant
• cons: Starting the qualification tool without going through the argProcessor will bypass all those checks.

[parthosa]

Yes, in that case, it will bypass those checks. If caller provides invalid value of QualFilterApp, the tool would crash instead of silently continuing with the default value. I think this should be the right behavior. I agree this differs from the original behavior.

[cindyyuanjiang]

Thanks @parthosa!