fix: replace bare except clauses with specific exception types

[rtmalikian]

Problem

Bare except: clauses catch KeyboardInterrupt, SystemExit, and GeneratorExit in addition to intended exceptions. This prevents graceful shutdown and makes debugging harder.

Affected Files

• pyhealth/metrics/ranking.py: except: should be except ImportError:
• pyhealth/calib/predictionset/scrib/quicksearch.py: except: should be except ImportError:
• pyhealth/datasets/base_dataset.py: two except: on queue.get(timeout=1) should catch queue.Empty

Proposed Fix

Replace each bare except: with the specific exception type it's intended to handle.