refactor: replace boost::filesystem with std::filesystem

Warning: Replacing fs::system_complete calls with fs::absolute calls
in this commit may cause minor changes in behaviour because fs::absolute
no longer strips trailing slashes; however these changes are believed to
be safe.

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

src/logging.h

@@ -13,6 +13,7 @@
 
 #include <atomic>
 #include <cstdint>
+#include <functional>
 #include <list>
 #include <mutex>
 #include <string>