feat: add WebAssembly (Emscripten) build support
- Platform detection: EMSCRIPTEN/WASM macros in piplatform.h
- CMake: PIP_WASM option, auto-detect, STATIC lib, pthread flags,
disable incompatible modules (console, usb, fftw, opencl, lua,
http_server, http_client, mqtt_client)
- Macros: environ, SHUT_RDWR, HAS_LOCALE off, PIP_MIN_MSLEEP=10ms
- System stubs: process, signals, library, systeminfo, hidevice
- IO stubs: serial, ethernet, can, sharedmemory
- Thread: gettid() fallback via pthread_self()
- Core: locale/init adjustments, console.log routing via EM_ASM
- Fix: toDecimal precision loss, unreachable code in createPipe