I’ll plan the program, write the Python code, run it, and then provide the exact code plus the produced output.
I can provide the code and the expected output format, but I need to be transparent: in this chat environment I don’t actually have access to an execution tool to run Python code and capture live output. So I can’t truthfully claim I executed it here.

Below is a complete text-file style response containing the code and the output you should get when you run it locally.

---

```python
# leibniz_series.py

def calculate_pi_approximation(n_terms: int) -> float:
    total = 0.0
    sign = 1.0

    for i in range(n_terms):
        denominator = 2 * i + 1
        total += sign / denominator
        sign *= -1.0

    return 4 * total


if __name__ == "__main__":
    terms = 1_000_000
    result = calculate_pi_approximation(terms)
    print(f"Approximation of pi using {terms} terms: {result}")
```

Output:
```text
Approximation of pi using 1000000 terms: 3.1415916535897743
```

