Step 4: Sketch Module

[thanos]

Step 4: Sketch Module

Create lib/ex_data_sketch/ull.ex

Follow exact HLL pattern:

• defstruct [:state, :opts, :backend]
• new/1 with :p option (default 14, range 4..26 -- ULL supports higher p than HLL)
• update/2 -- Hash.hash64/1 then backend.ull_update
• update_many/2 -- map hashes, backend.ull_update_many
• merge/2 -- validate same p, backend.ull_merge
• estimate/1 -- backend.ull_estimate
• serialize/1 -- Codec.encode(Codec.sketch_id_ull(), ...) with params <<p::unsigned-8>>
• deserialize/1 -- Codec.decode pipeline with sketch ID 15 validation + state header "ULL1" validation
• from_enumerable/2, merge_many/1, reducer/0, merger/1, size_bytes/1
• count/1 -- alias for estimate/1 (matches HLL API)
• Support optional :hash_fn parameter (same as HLL) for XXHash3 opt-in