Context Manager — Timer

Implement a Timer context manager class with __enter__ and __exit__ that measures elapsed time.

• __enter__ records the start time and returns self.
• __exit__ records the end time and stores elapsed seconds in self.elapsed.
• Does not suppress exceptions.

with Timer() as t:
    time.sleep(0.1)
print(t.elapsed)  # ≈ 0.1

Implement solve() that:
1. Uses Timer to measure a time.sleep(0.05) block.
2. Returns True if elapsed >= 0.04 (accounting for system variance), False otherwise.

The checker also tests Timer directly with a controlled clock: returning
the same instance from __enter__, measuring elapsed time on normal exit,
and recording elapsed time while propagating the original exception. Use
time.perf_counter() to read the clock.