Add a helper function to check if a parameter is given or not

[seisman]

Motivation

In PyGMT, most parameters default to False (for boolean-only parameters) or None (for non-boolean parameters), which means the parameters are not given and should not be used in building the CLI option string. We usually need to check if a parameter is given, like below

if value is not False:  # For boolean-only parameters
   ...

if value is not None:  # For non-boolean parameters
   ...

if value is not None and value is not False:  # A more general check
   ...

This repetitive pattern:

• Reduces code readability
• Makes maintenance harder [Sometimes we may incorrectly use if value is not None when value is a boolean type]
• Makes the intent less clear to new contributors

Solution

Introduced a new is_given() helper function to simplify parameter validation across PyGMT and refactored existing code to use it consistently.

def is_given(value: Any) -> bool:
    return value is not None and value is not False

Then we should

• replace x is not None/x is not False/x is not None and x is not False with is_given(x).
• replace x is None or x is False to not is_given(x)

This is just an internal change and doesn't break any existing behavior.

Comments?