Redesign IIC pfsConfig handling to avoid faking pfsConfig and detect pfsDesign mismatches early

The current IIC pfsConfig handling can implicitly generate a fake pfsConfig when none is found (e.g. when moveToPfsDesign was not called). This allows data acquisition to proceed, but it's not consistent with the actual position of the cobras which can be mis-leading.

• Stop implicitly faking pfsConfig from pfsDesign in nominal operation.
• Always hold on the last known valid pfsConfig representing the physical cobra state.
• Detect and raise an explicit error when the declared pfsDesign does not match the current pfsConfig.
• Add an explicit bypass mechanism (optional forcePfsConfig) for tests or engineering use cases where cobras must not be moved.
• bias, dark, test exp_type can automatically use that bypass.
• Clearly define and isolate special cases such as moveToHome( including with noMCSExposure option)

This redesign would allows us to detect pfsConfig errors earlier and preserves correct book-keeping. At the same time, it keeps the flexibility needed for tests and special operations without silently masking real issues.