Fix Generator vmin_pu/vmax_pu setters not persisting to C engine

[matheusduartedm]

Summary

• Bug: dss.generators.vmin_pu and dss.generators.vmax_pu property setters call GeneratorsF with C API indices 11/13, but the C library handler for those indices doesn't write to the active Generator object — it only echoes the parameter back. This causes silent data corruption in power flow results (OpenDSS uses defaults 0.90/1.10 instead of the intended values).
• Fix: Replace the broken C API calls in _vmax_pu_write and _vmin_pu_write with text command workarounds (Generator.<name>.Vmaxpu=<value> / Vminpu=<value>), following the same pattern used elsewhere (e.g., LoadShapesV.py, SettingsV.py).
• Read operations (indices 10/12) are unaffected and remain unchanged.

Reproduction

dss.generators.name = "sgen_0"
dss.generators.vmin_pu = 0.0

# Getter looks OK:
print(dss.generators.vmin_pu)                    # → 0.0

# But the C engine was NOT updated:
print(dss.text("? Generator.sgen_0.Vminpu"))     # → 0.90 (default!)

After this fix, the text command correctly returns 0.0.

Root cause

The bug is in the OpenDSS C library (libOpenDSSC.so), not in py-dss-interface's Python code. The GeneratorsF function handler for parameter indices 11 and 13 reads the argument but doesn't assign it to the active Generator's Vmaxpu/Vminpu fields. The equivalent DSSLoadsF handler (indices 29/35) works correctly for loads.

Test plan

• Verified fix with manual test: set vmin_pu=0.0, vmax_pu=2.0, confirmed via text command read-back
• Existing tests in test_generators.py (note: test suite has pre-existing setup issues on Linux due to missing .so in linux/cpp/ directory — not related to this change)

[PauloRadatz]

Hi @matheusduartedm, thank you so much for reporting this issue. I replicated it on my side. I will work on fixing it in the OpenDSS source code.

Please let me know if you have seen this in other properties.

Again, thank you so much.

[PauloRadatz]

I just noticed that this type of issues is not related to generators and C++ version. It is in some elements and also in Delphi. I will need to work on the OpenDSS source codes (Delphi and C++).