[LimaniBhavik]

The Black-Scholes formula and its associated Greeks calculations are vulnerable to division by zero and undefined logarithm errors if inputs like strike price, spot price, time, or volatility are zero or negative.

This PR addresses these issues by:

• Modifying calculate_call_option_price to return an error if s, k, t, or sigma are <= 0.0.
• Modifying calculate_greeks to return an error if s, k, t, or sigma are <= 0.0.
• Ensuring that the risk-free rate r is still allowed to be zero or negative.

These changes prevent NaN or Infinity from being returned, improving the security and reliability of financial calculations.

---

PR created automatically by Jules for task 3235818482938361948 started by @LimaniBhavik

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.