133. ClassNames / clsx

Implement classNames(...args), a small utility similar to classnames or clsx.

1. Accepted Inputs

• Strings and numbers should be included.
• Arrays should be flattened recursively.
• Objects should include keys whose values are truthy.
• Falsy values like false, null, undefined, 0, and '' should be ignored as standalone arguments.

2. Output

• Return one space-separated string.
• Preserve argument order.
• Do not add extra spaces.