"""Creates a detailed diff message between two texts.

This function compares two input texts, `optim_text` and `incr_text`, and generates a message highlighting the lines that are unique to each text. The comparison is performed using `difflib.ndiff`, which identifies lines that are added, removed, or unchanged between the two texts.

Args:
    optim_text (str): The first text to compare, typically representing an optimized version.
    incr_text (str): The second text to compare, typically representing an incremental version.

Returns:
    str: A formatted message that lists lines unique to `optim_text` under "Only in optimized prompt" and lines unique to `incr_text` under "Only in incremental prompt". Each line is indented for clarity.
"""