Add missing libc.prx symbols required by Unity IL2CPP runtime:
- Implement _Dtest double classification in Math.cpp
- Implement _Inf double constant in Math.cpp
- Implement sceLibcBacktraceGetBufferSize and sceLibcBacktraceSelf in Backtrace.cpp
- Implement _Cnd_signal in Threads.cpp
- Implement _ZNSt8ios_base7_AddstdEPS_ in RuntimeSupport.cpp
- Implement __pointer_type_info and __function_type_info vtables in TypeInfo.cpp
- Remove duplicate stubs from libSceAmpr/Export.cpp
- Add unit tests in GuestMath.cpp and GuestLibcThreads.cpp
- Document unverified behaviors in docs/dev/debt/libc.md
hamb3r
MarcZX100
David