Feature Request: Support strict parameter filtering (exclude non-matched parameters from merging)

Current Behavior

When specifying filters in the config, I expected only the matched parameters to be merged, and all other parameters to remain identical to the base_model.

However, from experiments and direct state_dict comparisons, it appears that:

Parameters matching filters are merged using the specified method (e.g., linear) But parameters NOT matching filters are still merged (likely using a default behavior), instead of being copied from the base model

This results in full-model blending, even when only partial merging is intended.

Evidence

I compared the merged model with a manually merged version where:

Only selected parameters (e.g., A_logs, x_proj_weight, dt_projs_weight) are averaged All other parameters are directly copied from the base model

The differences show that many non-filtered parameters (e.g., backbone layers, normalization, head, even control buffers like scan_direction) are modified in MergeKit output.

This leads to significant performance degradation in my case.