Add Default Precision 0 to ROUND Function

[vineetg3]

Description:

Currently, the ROUND function in PyDough requires the user to explicitly provide a precision argument. However, Python's built-in round() function defaults to a precision of 0 when no precision is specified. To ensure consistency and make the ROUND function more user-friendly, its behavior should be updated to align with Python's round() by defaulting the precision to 0.

Proposed Solution:

• Update the ROUND function implementation to make the precision argument optional.
• If no precision is provided, default to 0.

Example:

Current Behavior:

ROUND(expression, 0)  # Users must explicitly provide the precision, e.g., 0 for rounding to the nearest integer.

New Behavior:

ROUND(expression)  # Defaults to ROUND(expression, 0)

• Ensure that this change is reflected in the documentation.