acpiv uses an incorrect chained comparison for validation (if S == I is None:)

[marcostfermin]

Describe the bug

acpiv() validates inputs using if S == I is None:, which is a chained comparison equivalent to (S == I) and (I is None). This is not the intended “too few args” check and can let invalid argument combinations slip through (or behave inconsistently).

https://electricpy.readthedocs.io/en/latest/_modules/electricpy.html

Reproduction Code

# Setup
import electricpy as ep

# Code which causes failure
# Only S is provided; I and voltages are missing.
# This should be rejected early as "too few arguments" / insufficient specification,
# but the current check is not actually checking "S is None and I is None".
try:
    ep.acpiv(S=550)
except Exception as e:
    print("Raised:", type(e).__name__, e)
else:
    print("No exception raised (unexpected for insufficient inputs).")

Expected behavior

A clear, deterministic validation error for insufficient inputs (e.g., ValueError) before later operations attempt to use missing values.

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. Linux]
• Python Version [3.11.6]
• Version [0.4.0]

Additional context

That line should almost certainly be something like:

if (S is None) and (I is None): ...
(or a fuller validation that enforces “exactly two of {S, I, V*} must be provided”, etc.).