tests: Fix thread_metric message processing

Changes the type of both the tm_message_sent and tm_message_received
arrays from 'unsigned long' to 'unsigned int'. The test expects those
arrays to be 16 bytes long. This was a problem on 64-bit platforms
as 'unsigned long' is 8 bytes, which made the arrays 32 bytes long.
On both our supported 32-bit and 64-bit platforms, 'unsigned int'
works out to be 4 bytes long, thereby giving us the requisite 16
byte buffer.

Although a case could be made for using 'uint32_t', this was not
chosen simply to keep the structure as close as practical to the
original thread_metric implementation.

Fixes #83864

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>