feat: add log levels to logger

Replace log_message with log_debug/info/warn/err and a level filter
controlled by logger_set_level. Extract the printf sink into
log_write so CMock can intercept it in test_logger. Add 9 tests
covering emit and suppression behaviour per level.

tests/test_report.c

@@ -6,22 +6,22 @@ void setUp(void)    { Mocklogger_Init(); }
 void tearDown(void) { Mocklogger_Verify(); Mocklogger_Destroy(); }
 
 void test_report_formats_label_and_value(void) {
-    log_message_Expect("count: 42");
+    log_info_Expect("count: 42");
     report_value("count", 42);
 }
 
 void test_report_negative_value(void) {
-    log_message_Expect("score: -5");
+    log_info_Expect("score: -5");
     report_value("score", -5);
 }
 
 void test_report_zero(void) {
-    log_message_Expect("total: 0");
+    log_info_Expect("total: 0");
     report_value("total", 0);
 }
 
 void test_report_calls_log_exactly_once(void) {
-    log_message_Expect("x: 1");
+    log_info_Expect("x: 1");
     report_value("x", 1);
 }