Add dbg_init/dbgprintln macros that write directly to /scheme/debug/no-preserve,
bypassing logd output redirection after switch_stdio. This enables scheduler
tracing (INIT_RUN, INIT_DEFER, INIT_BLOCK, INIT_DONE, INIT_SCHEME) to remain
visible on the serial console throughout all boot phases.
Also add INIT_SPIN counter to detect infinite polling loops in step().
Red Bear OS