sketch_misra_gries.nx

sketch_misra_gries.nx -- Misra-Gries frequent items (1982). Bounded set of (key, count) pairs of capacity (k-1). On arrival of (key, w): - if key tracked: count[key] += w - else if free slot: install (key, w) - else: decrement EVERY counter by w (with floor 0); counters that reach 0 are freed for future use GUARANTEE (different from SpaceSaving): true_count - N/k <= estimate <= true_count Misra-Gries UNDERESTIMATES; SpaceSaving OVERESTIMATES. Both bound the error by N/k. Symmetric error semantics let callers pick: - SpaceSaving for upper-bound queries ("at most X") - Misra-Gries for lower-bound queries ("at least X") CAPABILITY STOMP vs DataSketches: DS ships only the "frequent items" variant (SpaceSaving-like). We ship BOTH algorithmic approaches (SpaceSaving + Misra-Gries) so callers pick by error-bound direction. LOSSLESS-LANGUAGE DISCIPLINE: nx_mg_query returns ApproxI64 with NX_ENV_ABS; param_a = N/k (the maximum possible UNDERESTIMATE); conf_ppb = 1e9 (deterministic).