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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def call_builder_init(cls, kb_app, sphinx_app: Sphinx):
 """ On builder init event, commit registry and do callbacks """


        # Find and commit docs project plugins
        conf_dir = sphinx_app.confdir
        plugins_dir = sphinx_app.config.kaybee_settings.plugins_dir
        full_plugins_dir = os.path.join(conf_dir, plugins_dir)

        if os.path.exists(full_plugins_dir):
            sys.path.insert(0, conf_dir)
            plugin_package = importlib.import_module(plugins_dir)
            importscan.scan(plugin_package)
        else:
            logger.info(f'## Kaybee: No plugin dir at {plugins_dir}')

        dectate.commit(kb_app)
        for callback in cls.get_callbacks(kb_app, SphinxEvent.BI):
            callback(kb_app, sphinx_app)