$.session.usage() plugin call now accepts and validates options

What The $.session.usage() call available to plugins previously took no arguments. It now accepts an optional options object with:

• breakdown, which must be 'summary' or 'full'
• columns, which must be a positive integer

A new validation step checks these values (and rejects unknown keys) before the call runs, instead of running unchecked.

Why Plugin authors get immediate, clear errors if they pass invalid options to session.usage(), instead of the call silently misbehaving or failing later.