Checkpoint: Metaprogramming

Checkpoint — instrument a class

Write @timed, a class decorator that wraps every public method (not starting with _) of the decorated class so that each call's wall time is appended to cls.__timings__[method_name] (a list, created on demand).

Requirements:

• method names stay correct on the wrapper (__name__ preserved)
• private/dunder methods are untouched
• works for any class (the decorator must not hardcode names)
• timings must accumulate across instances

This is the exact pattern profilers, metrics libraries, and tracing hooks use when they cannot ask you to edit every method.