Create unit tests for all functions related to M/M/s models in queueing_theory.py.
Solve issues identified by unit tests, specifically by ensuring functions now raise exceptions for invalid input conditions such as negative inputs for lambda and miu and when the system is unstable.
Address SonarLint naming convention warnings in the M/M/s functions within queueing_theory.py.
issue
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queueing_theory.py.