feat: add multiMonth prop to display months as scrollable list #218

[yasaricli]

Adds a new multiMonth prop to DateTimePicker that renders all months between minDate and maxDate in a vertically scrollable list. This is ideal for range selection across multiple months, similar to booking or travel date pickers. #218

Changes

• Added multiMonth boolean prop to DatePickerBaseProps
• When multiMonth is enabled, months are derived from minDate and maxDate (falls back to current month + 12 months if not provided)
• Added CHANGE_DATE_ONLY reducer action to prevent currentDate from being overridden when month prop is explicitly set — fixes incorrect date highlighting across months
• Updated README with usage documentation and example
• Added multi-month example screen to the example app