kv: mark kvnemesis tests as "large" sized

We've recently seen these time out exclusively on eng flow. In all
those instances, we can see the test is making some progress from
the stack traces -- it's slow though. We mark KVNemesis tests as
large, which in turn bumps their timeout in CI.

Closes cockroachdb#118624
Closes cockroachdb#118005

Release note: None

pkg/kv/kvnemesis/BUILD.bazel

@@ -60,7 +60,7 @@ go_library(
 
 go_test(
     name = "kvnemesis_test",
-    size = "medium",
+    size = "large",
     srcs = [
         "applier_test.go",
         "engine_test.go",