Add test cases for consistent cache behavior

Using `rand.intn` test cases as template, we create similar tests
that verify consistent values returned by `uuid.rfc4122` and `time.now_ns`
builtins when invoked during the same evaluation/query.

These tests can also aid compliance regression testing for other OPA implementations,
such as Swift.

Signed-off-by: Dmitry Frenkel <d_frenkel@apple.com>

v1/test/cases/testdata/v1/time/test-time-0972.yaml

@@ -0,0 +1,13 @@
+---
+cases:
+  - note: time.now_ns/consistent value for same evaluation
+    query: data.test.p = x
+    modules:
+      - |
+        package test
+
+        p := count(times) if {
+        	times := {time.now_ns() | numbers.range(1, 100)[_]}
+        }
+    want_result:
+      - x: 1

v1/test/cases/testdata/v1/uuid/test-uuid-rfc4122.yaml

@@ -0,0 +1,13 @@
+---
+cases:
+  - note: uuid.rfc4122/consistent values for same arguments
+    query: data.test.p = x
+    modules:
+      - |
+        package test
+
+        p := count(uuids) if {
+        	uuids := {uuid.rfc4122("key") | numbers.range(1, 100)[_]}
+        }
+    want_result:
+      - x: 1