docs: fix language errors

[loama]

What

Fixes three objective language errors in the published NeuralForecast documentation.

Why

The current pages contain duplicated words and one incorrect verb agreement. These mistakes are visible in the rendered capability, tutorial, and TFT model pages.

How

1. Remove duplicated “the” and “and.”
2. Change “It transform” to “It transforms.”
3. Keep the surrounding technical meaning unchanged.

Testing

1. Parsed both modified notebooks as valid JSON.
2. Reviewed the complete Markdown and notebook diff.
3. Confirmed no credentials or generated artifacts are included.

Checklist

1. The title follows the conventional commit format.
2. The pull request is focused on one concern.
3. The complete diff was reviewed.
4. No secrets, credentials, or personal data are included.

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