Step 5: Rust NIF

[thanos]

Step 5: Rust NIF

Create native/ex_data_sketch_nif/src/ull.rs

Three NIF operations (matching HLL pattern):

• ull_update_many_impl -- iterate packed u64 hashes, compute ULL register values, max-update register array
• ull_merge_impl -- register-wise max (identical logic to hll_merge_impl)
• ull_estimate_impl -- FGRA estimator in Rust (f64 arithmetic, sigma/tau convergence loops)

Entry points: ull_update_many_nif + _dirty_nif, ull_merge_nif + _dirty_nif, ull_estimate_nif + _dirty_nif

Modify native/ex_data_sketch_nif/src/lib.rs -- add mod ull;