Extend cycle to cycle error check for closed-loop models

Problem

In https://github.com/SimVascular/svZeroDSolver/pull/109, code was added to check for cycle-to-cycle convergence for an open-loop 0D model. To do so, it tracks cycle-to-cycle changes in mean pressure and flow at vessel caps, which seem to be limited to connections between vessels and boundary_conditions. For closed-loop model, there are no boundary_conditions, so the periodicity check does not work.

Solution

Modify the periodicity check to consider inlets and outlets of all vessels, regardless of if they are connected to boundary conditions.

Additional context

@mrp089 @menon-karthik was there a reason this periodicity check was originally limited to vessel-boundary_condition connections?

Code of Conduct

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

Start by locating the periodicity check introduced in PR #109 and trace how it finds vessel-cap connections. Verify the behavior with a closed-loop 0D model and confirm that cycle-to-cycle mean pressure and flow are checked at every vessel inlet and outlet, including cases without boundary_conditions.