Infer input type.
TItem extends BaseSchema<unknown, unknown, BaseIssue<unknown>>
| BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>
| BaseValidation<any, unknown, BaseIssue<unknown>>
| BaseValidationAsync<any, unknown, BaseIssue<unknown>>
| BaseTransformation<any, unknown, BaseIssue<unknown>>
| BaseTransformationAsync<any, unknown, BaseIssue<unknown>>
| BaseMetadata<any>
NonNullable<TItem["~types"]>["input"]