Add Chamber model with nonlinear filling behavior

[zinanhu0810]

Problem

All existing chamber blocks in svZeroDSolver assume linear (or effectively linearized) filling in diastole, typically via a time-varying elastance form P(t)=E(t)[V(t)−Vrest(t)].
This makes it hard to reproduce well-established nonlinear P–V behavior in atria/ventricles during filling.

Solution

Implement a new chamber model with nonlinear passive filling behavior using exponetial equation.

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct and Contributing Guidelines