[common] introduce bit_utils.hpp for bit manipulation (#11884)

This commit introduces a new header file, `common/bit_utils.hpp`, to
consolidate bit manipulation utility functions.

These functions were previously located in `common/num_utils.hpp`.
Moving them to a dedicated file improves code organization and
clarity by separating them from general numerical utilities. All
files that used these functions have been updated to include the new
header.

tests/unit/test_serial_number.cpp

@@ -31,6 +31,7 @@
 #include <openthread/config.h>
 
 #include "test_util.h"
+#include "common/bit_utils.hpp"
 #include "common/code_utils.hpp"
 #include "common/num_utils.hpp"
 #include "common/numeric_limits.hpp"