Return `EmptySolution` instead of raising `SolverError` for IDAKLU convergence failures

[BradyPlanden]

Description

The current IDAKLU multithreading implementation (#4087) raises a SolverError if any of the solution objects have IDAS failures, preventing multithreaded parameter inference workflows from continuing when some proposals fail to converge.

This issue proposes that a "failure" termination is added to the solver and an EmptySolution object is returned alongside a user warning instead of the SolverError.

Motivation

No response

Possible Implementation

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Additional context

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[MarcBerliner]

@BradyPlanden great idea! If I may make one suggestion, we could make a solver option named "on_failure" (to match "on_extrapolation") which either:

• throws the error
• returns a partial solution (and warns the user)
• returns an empty solution (and maybe ignores the error)