fix: Support finishReason in both new and old versions of ai-sdk

[alexgleason]

What does this PR do?

Enables both new and old versions of ai-sdk providers to work with the new finishReason property introduced in vercel/ai#11338

Fixes #7439 #7674

How did you verify your code works?

I created a custom npm package based on @ai-sdk/openai-compatible. Before the change I was getting a zod error. After the change it works.

[github-actions]

Hey! Your PR title Support finishReason in both new and old versions of ai-sdk doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[tzssangglass]

work for me, I built opencode with this PR locally, and no more errors like: #7439

[github-actions]

Closing this pull request because it has had no updates for more than 60 days. If you plan to continue working on it, feel free to reopen or open a new PR.