some persona skins are insanely bloated and get split into hundreds of parts.
it's quite annoying that we have to accommodate this, but we can't keep allowing players to experience login timeouts without an obvious indication what's wrong.
until now, any thread crash would show as a generic crash since we aren't able to get the trace from the crashed thread directly. This uses some dirty tricks to export a partially serialized stack trace to the main thread, where it can be written into a crashdump.
This enables us to see proper crash information for async tasks in the crash archive (finally!!!) as well as being able to capture RakLib errors properly.
this was previously part of the abandoned package pocketmine/spl. It had to be separated in the PM3 days, because RakLib depended on it.
Since RakLib 0.13, RakLib stopped being dependent on or aware of pthreads, so it no longer depends on any thread-related packages.
It's also possible to absorb pocketmine/snooze and pocketmine/classloader back into the core with this in mind.
I previously avoided this due to being unsure of the effects; however, it's clear that we already use typed properties on Threaded things in other places anyway, and the only known issues are with uninit properties, and arrays.
this gains a very small performance improvement by avoiding unnecessary !== null checks on every packet written in either direction. It's insignificant for sure, but I just found this code in an old stash, so what the heck.
at this point it's really not much more than just a thread-safe way to transmit parameters from main to thread. Maybe we can ditch it in favour of a generic closure-based thread implementation.
