Address PR feedback: add further test cases

pkg/streamingpromql/testdata/ours/functions.test

@@ -196,12 +196,19 @@ eval instant at 54m scalar(multiple_series)
 clear
 
 load 6m
-  metric{series="float"} 1 2 3 4 -5
+  metric{series="float"} 1 2 3 4 -5 0 NaN -NaN
   metric{series="histogram"} {{schema:3 sum:4 count:23 buckets:[1 2 4] n_buckets:[3 5 8]}} {{schema:3 sum:14 count:27 buckets:[1 2 6] n_buckets:[3 5 10]}}
 
 # Unary negation of a native histogram currently does nothing in Prometheus' engine, which seems incorrect, but we mirror its behaviour for consistency.
 # See https://github.com/prometheus/prometheus/pull/14821 for more discussion.
-eval range from 0 to 24m step 6m -metric
-  {series="float"} -1 -2 -3 -4 5
+eval range from 0 to 42m step 6m -metric
+  {series="float"} -1 -2 -3 -4 5 0 -NaN NaN
   {series="histogram"} {{schema:3 sum:4 count:23 buckets:[1 2 4] n_buckets:[3 5 8]}} {{schema:3 sum:14 count:27 buckets:[1 2 6] n_buckets:[3 5 10]}}
 
+clear
+
+load 1m
+  metric 1 _ _ 3 _ stale 4 _
+
+eval range from 0 to 7m step 1m -metric
+  {} -1 -1 -1 -3 -3 _ -4 -4