PR: Add option to save files atomically in the SaveFileManager

[jnsebgosselin]

This PR adds an option to perform atomic file saves in the SaveFileManager class.

Atomic saving first writes data to a temporary file, then replaces the target file in a single operation. This minimizes the risk of data loss or corruption from partial writes. The new atomic flag allows users to enable or disable this behavior as needed, with backward compatibility preserved.

Includes:

• New atomic parameter for SaveFileManager
• Updated save logic to support atomic file operations
• Tests for both atomic and non-atomic save modes

Atomic writes (or atomic saving) refer to a file-saving strategy where data is first written to a temporary file and, upon successful completion, the temporary file is moved or renamed to replace the original file in a single operation. This ensures that the file is never left in a partially written or corrupted state: the update either happens completely, or not at all. Atomic saving increases data integrity and safety, especially in the event of program crashes or interruptions during the save process.