CH-Earth/summa: Experimental v4.4.0 support model calibration and objective-function workflows

This PR refactors SUMMA's simulation and parameter setup to support model calibration and objective-function workflows while preserving the existing simulation behavior.

Refactors parameter setup into initialization, parameter assignment/override, and parameter-dependent update stages.

• Adds command-line parameter overrides using repeatable --param <name> <value> arguments.
• Introduces a reusable simulation interface that returns simulated time and streamflow directly to the caller.
• Separates the generic simulation lifecycle from SUMMA-specific timestep execution, simplifying the MPI driver and enabling reuse by optimization workflows.
• Adds access to mizuRoute streamflow at the configured outlet reach.
• Preserves the existing forcing, physics, output, restart, and parameter-processing workflows.
• Maintains bit-for-bit agreement with the existing SUMMA implementation when parameter overrides are not used.

These changes provide the foundation for evaluating SUMMA as a callable model function, where a parameter vector can be supplied and the corresponding simulated streamflow returned directly. This will support subsequent implementation of objective functions and parallel parameter-estimation workflows without requiring model results to be exchanged through output files.

What's Changed

• Merges #637 (objective function and parameter overrides) into the spatial-dimension (dom / glacier / lake / grid) code by @ashleymedin in https://github.com/CH-Earth/summa/pull/646
• Feature/objfunc by @martynpclark in https://github.com/CH-Earth/summa/pull/637

Full Changelog: https://github.com/CH-Earth/summa/compare/v4.3.0-exp...v4.4.0-exp