[python-fastapi] Check regex pattern on array items

[rgroothuijsen]

When a model field is an array rather than a single value, no regex check is performed on the array's items even if the OpenAPI spec defines one. This adds a per-item check to a field if it is an array, based on the existing code used to validate single values. Given the provided test case, the result would look like this:

@field_validator('tags')
def tags_items_validate_regular_expression(cls, value):
    """Validates the regular expression"""
    if value is None:
        return value

    for item in value:
        if item is None:
            continue

        if not re.match(r"^[A-Z0-9_\- ]+$", item):
            raise ValueError(r"must validate the regular expression /^[A-Z0-9_\- ]+$/")
    return value

Fixes #23102

@cbornet @tomplus @krjakbrjak @fa0311 @multani

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---

Summary by cubic

Add per-item regex validation for array fields in python-fastapi models so item patterns from the OpenAPI spec are enforced at runtime. Fixes #23102.

• Bug Fixes
  • Generate an item-wise @field_validator for array fields that applies the item regex (incl. nullable handling and regex modifiers).
  • Process item patterns in codegen by calling postProcessPattern on property.items.
  • Add test testRegexPatternCheckedForArrayItems using 3_1/issue_23102.yaml.

^{Written for commit f75cf04. Summary will update on new commits.}

[cubic-dev-ai]

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