lang/micropython: upgrade to 1.28.0

• Add mbedtls and micropython-lib submodules via GH_TUPLE
• Use POSIX semaphores for mp_thread_mutex_t to fix cross-thread unlock on FreeBSD (PTHREAD_MUTEX_ERRORCHECK rejects non-owner unlock with EPERM)
• Remove -Werror from mpy-cross and unix port Makefiles
• Fix select_poll_fd test: FreeBSD poll(2) checks kern.maxfilesperproc (not RLIMIT_NOFILE), so print SKIP instead of assert False when 6000 fds do not trigger EINVAL
• Update ffi test patches for FreeBSD libc.so.7
• Compile ffi_lib.so in pre-test for ffi_int_* tests