parallel-workload: Don't use uuid_generate_v5

also generate larger expressions

Seen failing in https://buildkite.com/materialize/nightly/builds/13939#019a35f7-b7e4-4f6d-b97a-4f9548e82422

Author: def-

misc/python/materialize/parallel_workload/expression.py

@@ -12,7 +12,6 @@
 
 from materialize.data_ingest.data_type import (
     DATA_TYPES,
-    UUID,
     Boolean,
     Bytea,
     DataType,
@@ -260,10 +259,11 @@ def __init__(self, text: str, params: list, unsupported: ExprKind = ExprKind.ALL
     FuncOp("list_cat({}, {})", [IntList, IntList]),
 ]
 
-FUNC_OPS[UUID] += [
-    FuncOp("uuid_generate_v5({}, {})", [UUID, Text]),
-    # FuncOp("cast({} as uuid)", [Text]),
-]
+# uuid_generate_v5 can return NULL
+# FUNC_OPS[UUID] += [
+#     FuncOp("uuid_generate_v5({}, {})", [UUID, Text]),
+#     # FuncOp("cast({} as uuid)", [Text]),
+# ]
 
 
 def expression(
@@ -277,7 +277,7 @@ def expression(
     level: int = 0,
 ) -> str:
     if level < 60:
-        if FUNC_OPS[data_type] and rng.random() < 0.5:
+        if FUNC_OPS[data_type] and rng.random() < 0.7:
             fnop = rng.choice(FUNC_OPS[data_type])
             if (
                 kind == ExprKind.ALL