internal/rosa/azalea: evaluator

Performance is sufficient for the use case, despite the fact that I could not even think of a lower-effort way to do this:

BenchmarkParse-128        	   55100	     21494 ns/op
BenchmarkEvaluate-128     	  131670	      9248 ns/op

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/azalea/azalea_test.go

@@ -154,3 +154,16 @@ func TestParse(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkParse(b *testing.B) {
+	r := strings.NewReader(sample)
+	for b.Loop() {
+		if _, err := Parse(r); err != nil {
+			b.Fatal(err)
+		}
+
+		b.StopTimer()
+		r.Reset(sample)
+		b.StartTimer()
+	}
+}