refactor: migrate MICRO_PIP to fine-grained feature flags

Replace monolithic MICRO_PIP/PIP_MICRO with granular flags:

Feature flags (CMake options + platform auto-detection):
- PIP_NO_FILESYSTEM, PIP_NO_THREADS, PIP_NO_SOCKET
- PIP_NO_PROCESS, PIP_NO_DYNLIB, PIP_NO_FFT, PIP_NO_SERIAL

Embedded optimization flag:
- PIP_EMBEDDED (auto-set for Pico SDK and FreeRTOS)
  Controls buffer sizes, time stubs, terminal fallback, init stubs

Platform blocks in CMakeLists.txt:
- Pico SDK: auto-disables FS, PROCESS, DYNLIB, FFT, SERIAL;
  conditionally disables THREADS (no FreeRTOS) and SOCKET (no LWIP)
- FreeRTOS: auto-disables FS, PROCESS, DYNLIB, FFT, SERIAL;
  conditionally disables SOCKET (no LWIP)
- Android: auto-disables PROCESS, DYNLIB, FFT

Updated 96 files across libs/, utils/, tests/, and CMakeLists.txt.
Builds verified for Linux (547 tests pass) and Pico SDK (100%).
Removed all MICRO_PIP and PIP_MICRO references (0 remaining).

libs/main/io_devices/pispi.cpp

@@ -43,11 +43,11 @@ REGISTER_DEVICE(PISPI)
 
 
 PISPI::PISPI(const PIString & path, uint speed, PIIODevice::DeviceMode mode): PIIODevice(path, mode) {
-#ifdef MICRO_PIP
+#ifdef PIP_NO_THREADS
 	setThreadedReadBufferSize(512);
 #else
 	setThreadedReadBufferSize(1024);
-#endif
+#endif // PIP_NO_THREADS
 	setPath(path);
 	setSpeed(speed);
 	setBits(8);