Bug: polyfactoryutils.helpers.flatten_annotation does not handle Optional properly

[sam-or]

Description

calling the flatten_annotation function with an optional annotation int | None/Optional[int] does not properly flatten the annotation, instead the result is [NoneType,[int]] (expected: [NoneType, int])

MCVE

# Your MCVE code here
@dataclass
class OptionalInt:
    i: Optional[int]

class OptionalIntFactory(DataclassFactory[OptionalInt]):
    __model__ = OptionalInt

results = list(OptionalIntFactory.coverage())

Steps to reproduce

Run the `<factory>.coverage()` function with any factory for a model that has an optional field

Logs

TypeError: unhashable type: 'list'

Release Version

2.12.0

Platform

• [X] Linux
• [ ] Mac
• [ ] Windows
• [ ] Other (Please specify in the description above)

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[sam-or]

I'll create a PR for this