[FEATURE] Relax vCg__E lower bound to allow zero and validate simulations

[camUrban]

Problem Statement

OperatingPoint currently validates that vCg__E (a scalar speed) is strictly greater than 0.0 (the lower bound is exclusive). It would be useful to allow vCg__E = 0.0 for hover or zero-speed cases, but it is unknown whether the solvers handle this correctly.

Location(s): pterasoftware/operating_point.py

Proposed Solution

1. Relax the vCg__E validation in OperatingPoint.__init__() to allow 0.0 (change the lower bound from exclusive to inclusive).
2. Update the docstring and any tests that assert the old exclusive bound.
3. Run simulations with vCg__E = 0.0 and verify they produce valid results without division-by-zero or other numerical issues.
4. If simulations break, investigate and fix the root causes rather than reverting the bound change.

Additional Context

This issue is referenced by a TODO comment in OperatingPoint.