fix(typescript-fetch): correct ToJSON/ToJSONTyped type signatures

[fangd1997]

Fix the incorrect parameter and return types in the generated ToJSON and ToJSONTyped functions for typescript-fetch models.

• modelGeneric/mustache, modelOneOf.mustache: Fix ToJSON signature from (json: any): Model to (value?: Model | null): any
• modelEnum.mustache: Fix ToJSONTyped signature from (value: any, ignoreDiscriminator: boolean): Enum to (value?: Enum | null, ignoreDiscriminator: boolean): any Also make ToJSON delegate to ToJSONTyped instead of a raw cast

Fixes #21005

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---

Summary by cubic

Fixes incorrect ToJSON/ToJSONTyped type signatures in typescript-fetch to match runtime behavior and improve type safety. All ToJSON functions now accept optional model values and delegate to ToJSONTyped; enum ToJSONTyped returns any and defaults ignoreDiscriminator to false (fixes #21005).

• Bug Fixes
  • modelGeneric.mustache, modelOneOf.mustache: change ToJSON from (json: any): Model to (value?: Model | null): any; delegate to ToJSONTyped.
  • modelEnum.mustache: make ToJSON call ToJSONTyped; change ToJSONTyped to (value?: Enum | null, ignoreDiscriminator: boolean = false): any.
  • Regenerated typescript-fetch samples to apply the new signatures and delegation, including enum files.

^{Written for commit 420421a. Summary will update on new commits.}

[fangd1997]

@wing328@TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @topce (2018/10) @akehir (2019/07) @petejohansonxo (2019/11) @amakhrov (2020/02) @davidgamero (2022/03) @mkusaka (2022/04) @joscha (2024/10) @KannaKim (2026/07) Could you take a look at this PR when you have a chance? Thanks!

[cubic-dev-ai]

All reported issues were addressed across 250 files

<sub>Note: This PR contains a large number of files. cubic only reviews up to 200 files per PR, so some files may not have been reviewed. cubic prioritizes the most important files to review.

Re-trigger cubic</sub>