Refactor request stack handling

1. refactor how requester configs are processed in formkit.vue. Removed the reactive Stacks array and onMounted initialization; introduced a computed requesterConfigs (filters props.config for items with requester and non-standalone types) and a deep, immediate watch that calls executeRequestStack when items change. executeRequestStack now accepts an items array iterator, making request execution respond to dynamic config updates and improving reactivity handling.
2. Replace the deprecated upload size prop with explicit width and height props (defaults 80). In the component, add autoCalcSize to compute icon/progress sizes, update template bindings and styles to use width/height, and adjust icon/progress sizing.