Add constraints to hnswlib in raft-bench-ann (#1949)

This PR adds a constraint for `hnswlib` search params such that `ef >= k`

Authors:
  - Divye Gala (https://github.com/divyegala)

Approvers:
  - Corey J. Nolet (https://github.com/cjnolet)

URL: #1949

python/raft-ann-bench/src/raft-ann-bench/constraints/__init__.py

@@ -38,3 +38,8 @@ def raft_ivf_pq_search_constraints(params, build_params, k, batch_size):
 def raft_cagra_search_constraints(params, build_params, k, batch_size):
     if "itopk" in params:
         return params["itopk"] >= k
+
+
+def hnswlib_search_constraints(params, build_params, k, batch_size):
+    if "ef" in params:
+        return params["ef"] >= k

python/raft-ann-bench/src/raft-ann-bench/run/conf/algos/hnswlib.yaml

@@ -1,8 +1,10 @@
 name: hnswlib
+constraints:
+  search: raft-ann-bench.constraints.hnswlib_search_constraints
 groups:
   base:
     build:
       M: [12, 16, 24, 36]
       efConstruction: [64, 128, 256, 512]
     search:
-      ef: [10, 20, 40, 60, 80, 120, 200, 400, 600, 800]
+      ef: [10, 20, 40, 60, 80, 120, 200, 400, 600, 800]