#25480 fix(typescript-fetch): modelOneOf template imports

modelOneOf template now generates import statements correctly when additionalProperties.fileNaming is set to 'camelCase' or 'kebab-case'.

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Summary by cubic

Fixes the typescript-fetch modelOneOf template so oneOf model imports use filenames that respect the fileNaming option (camelCase or kebab-case) instead of always defaulting to PascalCase, which previously produced broken import paths.

The generator now builds a deduplicated import list pairing each model's class name with its correctly cased filename, so types used both directly and as array items are imported only once. Tests cover oneOf, array, and discriminator responses for both kebab-case and camelCase file naming.