Request help with new model development ``IEEEG1PW``

[jinningwang]

Is your feature request related to a problem? Please describe.

Implement PowerWorld - IEEEG1 by extend the existing IEEEG1 with a piecewise block GV

Describe the solution you'd like

A ready-to-run example is: https://github.com/CURENT/demo/blob/master/demo/IEEEG1PW/IEEEG1PW.ipynb

My trouble:

1. Failed to fix TDS initialization error of Piecewise GV

I also tried set self.IAW.y.v_iter = self.GV.y.e_str to catch the adjusted IAW_y, but didn't work

Overview of my implementation:

1. Refactor IEEEG1Model into three subclasses, IEEEG1SpeedControl, IEEEG1ValvePosition, and IEEEG1Turbine
   https://github.com/jinningwang/andes/blob/2af50bd1ac1810aafd452dc2ac2897b459479ab6/andes/models/governor/ieeeg1.py#L304-L309

2. Change ConstService v0 into PostInitService to store changed IAW_y
   https://github.com/jinningwang/andes/blob/2af50bd1ac1810aafd452dc2ac2897b459479ab6/andes/models/governor/ieeeg1.py#L248

3. Add class IEEEG1PWData to include the six pairs points
   https://github.com/jinningwang/andes/blob/2af50bd1ac1810aafd452dc2ac2897b459479ab6/andes/models/governor/ieeeg1.py#L419-L434

4. Add Piecewise GV
   https://github.com/jinningwang/andes/blob/2af50bd1ac1810aafd452dc2ac2897b459479ab6/andes/models/governor/ieeeg1.py#L460-L474

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