createPluginModule and PluginModuleDeps were exposed at package entry as
a test seam. Their export creates accidental public TS API obligations
for internal manager/tool/hook constructor types. Move to
src/testing/create-plugin-module.ts so only tests reach them.
Closes HIGH-8
Co-authored-by: api-surface (deep / gpt-5.3-codex high)
YeonGyu-Kim