ashes (Python dust) partials must include the .dust extension in the partial reference

The Python 'ashes' templating library (dust.js dialect) registers templates loaded by AshesEnv(['dir']) under their full filename including the extension. A dust partial reference written the canonical dust.js way, {>my_partial/}, raises TemplateNotFound because the registered name is 'my_partial.dust'. Fix: reference the partial with the extension: {>my_partial.dust/} (quoted form {>"my_partial.dust"/} also works). Easy to miss because template rendering calls (env.render('page.dust', ctx)) naturally include the extension, so the mismatch only surfaces for partial references inside templates.