move test fns outside of top level index to fix filter and slice errors (#10)

A user reported that "/opencode-warp@0.1.1 crashes on startup hooks with errors like "parts.filter is not a function" and "str.slice is not a function"." 

Both of these errors seem to be coming from test helper functions that are exported from the top level index.ts fn in our plugin module. [In older versions of opencode](anomalyco/opencode#13543), each function exported out of a module is automatically called as a plugin builder, so it makes sense that these functions would cause compilation errors because they are not meant to be called as plugin builders.

The fix is just to move the helper functions to their own util file.

Author: harryalbert

node_modules/.package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "@warp-dot-dev/opencode-warp",
-  "version": "0.1.4",
+  "version": "0.1.5",
   "description": "Warp terminal integration for OpenCode — native notifications and more",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",