Convert drt_model_instantaneous.m to MATLAB R2025b

[ludde017]

Convert drt_model_instantaneous.m to MATLAB R2025b

Summary

@ncohn
This PR adds a MATLAB R2025b-compatible version of the morphology-resolving dune response model to maintain compatibility for users working in newer MATLAB releases.

This PR is submitted on behalf of @Volk3rJ from LimnoTech.

What changed

• adds drt_model_instantaneous_R2025b.m
• specifically updates the morphology-resolving model implementation to use max, min, and sum with the 'omitnan' option in place of older nan* helper calls
• replaces the normal CDF call with an equivalent error-function-based formulation for collision probability
• keeps the existing reduced morphology-resolving workflow and example data intact while adding an R2025b-compatible model path
• adds comments to drt_run on how to use R2025b version.

Notes for maintainers

• the major change in this PR is the new R2025b-compatible model file
• the compatibility edits are focused on NaN-aware aggregation/interpolation support and the probability calculation used in the erosion routine
• no broader workflow restructuring is intended in this update

Things to double check

• run the morphology-resolving example workflow with MATLAB R2025b

• confirm the example completes without errors related to nanmax, nanmin, nansum, or cdf

• compare key outputs against the pre-R2025b workflow to verify expected behavior

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