[FEAT]: Global default for variation

### Description I've been looking at this upcoming PR: https://github.com/shinokada/svelte-heros-v2/pull/21 Thinking it would be useful to be able to control the solid | outline | mini defaults at a global level rather than having to apply "solid" to every image. Something like this could work: SvelteHeroes.defaultVariation = SvelteHeroes.solid; Likewise setting the size globally could also be useful. Cheers, Matt ### Additional Information _No response_