Type Error for python<=3.9

[Jack0Chan]

| operation is supported for python>=3.10, and we are fixing it by converting type a | type b into Union(type a, type b). We will fix this bug in version 1.2.1.

In addition, the fault_diagnosability() function is of exponential complex, and we have optimized it for scalability. For a model with $10^8\sim 10^{10}$ states, before optimization: over 20h, after optimization: within 100s.