feat: add custom Datastar.js configuration support

Allow users to provide their own Datastar.js script (e.g., Datastar Pro
or custom builds) via Via's Options configuration. Adds DatastarConfig
struct with Content ([]byte) and Path (string) fields.

h/h.go

@@ -79,7 +79,6 @@ func HTML5(p HTML5Props) H {
 		Body:        retype(p.Body),
 		HTMLAttrs:   retype(p.HTMLAttrs),
 	}
-	gp.Head = append(gp.Head, Script(Type("module"), Src("/_datastar.js")))
 	return gc.HTML5(gp)
 }