fix(responses): correct finalResponse error message and drop duplicate spread

[pouyashahrdami]

What

Two small fixes in the handwritten Responses helpers (src/lib/):

1. ResponseStream.finalResponse() reported the wrong type. When the stream ends without producing a result, it threw OpenAIError('stream ended without producing a ChatCompletion') and its JSDoc read ...without producing a REsponse. This helper returns a Response, not a ChatCompletion — the message was copied from the Chat Completions helper. Corrected both the thrown message and the doc typo.

2. Removed a redundant duplicate ...toolCall spread in ResponsesParser.parseToolCall. The object literal spread toolCall twice ({ ...toolCall, ...toolCall, parsed_arguments }). Spreading the same object twice is identical to spreading it once, so this is a pure no-op cleanup. It has been present since the file was first added.

Why

The ChatCompletion wording is misleading when debugging Responses streaming, and the duplicate spread is dead code.

Testing

• prettier --check and eslint pass on both files.
• tsc typechecks cleanly.
• Existing tests/lib/ResponseStream.test.ts and tests/lib/ResponsesParser*.test.ts suites pass.

No behavioral change beyond the corrected error string.

[pouyashahrdami]

Closing in favor of #2022, which already fixes the same finalResponse() error message and docstring typo (and does more). The only unique piece here was a no-op duplicate-spread cleanup, not worth a separate PR.