Implement reflection-based WhichMax and WhichMin to dynamically find the index or key of the maximum/minimum element in slices, arrays, or maps. Functions validate orderability, handle empty collections, and dispatch via reflect.Kind. Expose as which_max and which_min GVal functions, with float64 type assertions for compatibility and preserved error handling.
Introduce generic and reflection-based utilities for filtering slices and maps by minimum/maximum thresholds, along with saturating subtraction. The `obiutils` package provides type-safe generic implementations alongside dynamic reflection dispatchers to handle arbitrary ordered and numeric types. These are exposed as GVAL expression functions in `obiseq`, extending the language's built-in filtering and numeric capabilities.