fix(cli): remove unused got-fetch dependency

[fujikky]

Summary

Remove the unused got-fetch dependency from @openapi-codegen/cli.

Why

• got-fetch is not imported anywhere in this repository (src, tests, docs). got itself is still used directly in getOpenAPISourceFile.ts and is kept.
• got-fetch@5.1.11 and 5.1.12 are affected by GHSA-f29h-pxvx-f335 (malicious release, fixed in 6.0.0+).
• cli/package.json declares "got-fetch": "^5.1.1", so an install without a lockfile (e.g. a consumer installing @openapi-codegen/cli) resolves to the compromised 5.1.12. The lockfile in this repository pins 5.1.10, which is not affected.

Removing the unused dependency eliminates that exposure.

Verification

• pnpm install --frozen-lockfile
• pnpm build
• pnpm check (tsc / eslint / prettier)
• pnpm test (27 files, 241 tests passed)

Follow-up: replacing got with native fetch

While looking into this, I noticed that got is only used in cli/src/core/getOpenAPISourceFile.ts (a plain GET/POST with headers, plus 401/404 handling for the GitHub source). This looks easy to replace with Node's native fetch (the repo already requires Node >= 20), which would also drop the whole got dependency tree.

A few things to take care of: fetch does not throw on non-2xx responses (so the HTTPError handling needs res.ok / res.status checks), got's default retry behavior goes away, and the URL tests would need nock v14+ (v13 cannot intercept native fetch).

I kept this PR focused on the security fix. If you are interested, I'm happy to open a separate PR for that.