Add tests for handling invalid log levels in SetLogLevel

Ensure that setting an invalid log level with SetLogLevel does not affect existing log behavior. Additional test cases verify that only appropriate log messages are displayed based on the current log level.

log_test.go

@@ -59,10 +59,17 @@ func Test_PlainTextLogs(t *testing.T) {
 
 func Test_MutedPlainTextLogs(t *testing.T) {
 	InitStoneLog(ERROR, false, true)
+
+	// This won't change the log level
+	SetLogLevel(-1)
+
+	// Following won't appear
 	Trace("This is a trace log")
 	Debug("This is a debug log")
 	Observation("This is an observation log")
 	Hypothesis("This is a hypothesis log")
+
+	// Until this one
 	Failure("This is a failure log")
 }