fix: use except Exception and is not None in data_selection/utils.py

[harshadkhetpal]

Summary

Two PEP8 / correctness fixes in data_selection/utils.py:

1. Bare except: → except Exception: — The import guard for transformers.mpu used a bare except: which silently catches KeyboardInterrupt and SystemExit. Since there is no re-raise, except Exception: is the correct choice — it catches all regular import errors while letting system signals propagate.

2. != None → is not None — PEP8 E711: comparisons to None should always use is / is not, not == / !=.

Changes:

# Before
except:
    mpu = None

# After
except Exception:
    mpu = None

# Before
if args.save != None:

# After
if args.save is not None:

Testing

No behavior change — style/correctness fixes only.