feat(python): validate Enum categories

[alexander-beedie]

Split-out from #13345, and contains only the category-validation checks.
Prevents creation of invalid Enums (eg: with categories of the wrong type or duplicate values).

Examples

Category type check:

pl.Enum([1.234, 5.678])
# TypeError: Enum categories must be strings; found 1.234

Category uniqueness check:

pl.Enum(["misc", "value", "value", "other"])
# ValueError: Enum categories must be unique; found 1 duplicates, eg: 'value'

[stinodego]

Apparently I am in a nitpicky mood today 😬

Nice to check for duplicates and stringiness, just some comments about the implementation though.

[alexander-beedie]

Apparently I am in a nitpicky mood today 😬

Didn't happen to make this your New Year's resolution?
Off to a good start if so! 🤣

[stinodego]

Good to merge if CI passes 👍