fix: cast size_t args in cpulimit_test.c

Add explicit (size_t) casts to suppress -Wtraditional-conversion
warnings throughout the test file:

- write() and read() count arguments: literal 1 -> (size_t)1
- locate_node/locate_elem offset and length arguments: literal 0
  -> (size_t)0
- init_process_table() hash_size arguments: integer literals ->
  (size_t)N
- malloc() size arguments: CMD_BUFF_SIZE, CMD_BUFF_SIZE+1,
  PATH_MAX -> (size_t) variants
- get_self_command() buffer-size argument: CMD_BUFF_SIZE ->
  (size_t)CMD_BUFF_SIZE

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: HiGarfield <32226909+HiGarfield@users.noreply.github.com>

Author: Copilot