feat: implement the bDS2-compatible core Lua API

docs/scripting/examples/utility.lua

@@ -0,0 +1,7 @@
+function main()
+    local project = bds.projects.get_active()
+    if project == nil then return { processed = 0 } end
+    local posts = bds.posts.get_all()
+    bds.report_progress({ current = #posts, total = #posts, message = "Complete" })
+    return { processed = #posts }
+end