CODE QUALITY: Duplicated default constants across modules

[Manideep3969]

Issue

Default error rates (0.0005, 0.01, 0.015), T2 times (150e-6), and gate durations (50e-9, 300e-9) are hardcoded in multiple files:

• cost_model.py lines 221-222, 316-317
• cutting.py lines 635, 644, 650
• utils.py lines 159-161, 172-173
• scheduling.py line 401

If one is updated, others may be missed.

Fix

Define these as module-level constants or a shared configuration dataclass in utils.py and import them everywhere.