feat: introduce LogLevel value object and improve logger API

- Replace LogLevel enum with a dedicated class that encapsulates
  log level representation.
- Add factory methods for creating Debug, Info, and Error levels.
- Add string conversion support through LogLevel::toString().
- Add equality comparison operators for LogLevel instances.

- Rename Logger::writeLog() to writeMessage().
- Add writeMessage() overload that uses the default log level.
- Implement actual file writing with error handling using core::Status.
- Improve logger documentation to reflect the updated API.

- Update logger tests to use the new LogLevel API.
- Move logger tests into the core test directory.
- Replace enum-based log level usage with LogLevel factory methods.
- Update test cases for the renamed writeMessage() method.

tests/logger/logger_test.cpp

@@ -8,33 +8,35 @@
 
 namespace {
 
+using namespace logger;
+
 void testLoggerCreation() {
-  logger::Logger logger("test.log", logger::LogLevel::Info);
+  Logger logger("test.log", LogLevel::info());
 
   assert(logger.getFileName() == "test.log");
-  assert(logger.getLogLevel() == logger::LogLevel::Info);
+  assert(logger.getLogLevel() == LogLevel::info());
 }
 
 void testWithLogLevel() {
-  logger::Logger logger("test.log", logger::LogLevel::Info);
+  Logger logger("test.log", LogLevel::info());
 
-  auto debugLogger = logger.withLogLevel(logger::LogLevel::Debug);
+  auto debugLogger = logger.withLogLevel(LogLevel::debug());
 
-  assert(logger.getLogLevel() == logger::LogLevel::Info);
-  assert(debugLogger.getLogLevel() == logger::LogLevel::Debug);
+  assert(logger.getLogLevel() == LogLevel::info());
+  assert(debugLogger.getLogLevel() == LogLevel::debug());
 
   assert(debugLogger.getFileName() == "test.log");
 }
 
 void testWithFileName() {
-  logger::Logger logger("old.log", logger::LogLevel::Info);
+  Logger logger("old.log", LogLevel::info());
 
   auto newLogger = logger.withFileName("new.log");
 
   assert(logger.getFileName() == "old.log");
   assert(newLogger.getFileName() == "new.log");
 
-  assert(newLogger.getLogLevel() == logger::LogLevel::Info);
+  assert(newLogger.getLogLevel() == LogLevel::info());
 }
 
 void testWriteLogSuccess() {
@@ -42,9 +44,9 @@ void testWriteLogSuccess() {
 
   file.throwIfExists();
 
-  logger::Logger logger(file.getFileName(), logger::LogLevel::Info);
+  Logger logger(file.getFileName(), LogLevel::info());
 
-  auto result = logger.writeLog(logger::LogLevel::Info, "Application started");
+  auto result = logger.writeMessage(LogLevel::info(), "Application started");
 
   assert(result.isSuccess());
   assert(result.getValue());
@@ -66,9 +68,9 @@ void testWriteLogFailure() {
 
   std::filesystem::create_directory(file.getFileName());
 
-  logger::Logger logger(file.getFileName(), logger::LogLevel::Info);
+  Logger logger(file.getFileName(), LogLevel::info());
 
-  auto result = logger.writeLog(logger::LogLevel::Info, "message");
+  auto result = logger.writeMessage(LogLevel::info(), "message");
 
   assert(result.isFailure());
   assert(!result.getError().empty());
@@ -81,11 +83,11 @@ void testMultipleWrites() {
 
   file.throwIfExists();
 
-  logger::Logger logger(file.getFileName(), logger::LogLevel::Info);
+  Logger logger(file.getFileName(), LogLevel::info());
 
-  auto first = logger.writeLog(logger::LogLevel::Info, "first message");
+  auto first = logger.writeMessage(LogLevel::info(), "first message");
 
-  auto second = logger.writeLog(logger::LogLevel::Error, "second message");
+  auto second = logger.writeMessage(LogLevel::error(), "second message");
 
   assert(first.isSuccess());
   assert(second.isSuccess());