refactor: rename PIP_NO_\* to PIP_HAS_\* with inverted logic

All feature flags now use positive naming (enabled by default):
- PIP_HAS_FILESYSTEM, PIP_HAS_THREADS, PIP_HAS_SOCKET
- PIP_HAS_PROCESS, PIP_HAS_DYNLIB, PIP_HAS_FFT, PIP_HAS_SERIAL

Preprocessor guards inverted:
- #ifndef PIP_NO_X → #ifdef PIP_HAS_X
- #ifdef PIP_NO_X → #ifndef PIP_HAS_X

CMake options default ON instead of OFF.
Platform blocks set flags OFF to disable features.

85 files transformed via Python script + 2 manual fixes.

libs/main/thread/pithreadpoolworker.cpp

@@ -21,7 +21,7 @@
 
 #include "pisysteminfo.h"
 
-#ifndef PIP_NO_THREADS
+#ifdef PIP_HAS_THREADS
 
 //! \addtogroup Thread
 //! \{
@@ -239,4 +239,4 @@ void PIThreadPoolWorker::threadFunc(Worker * w) {
 	w->notifier.notify();
 }
 
-#endif // PIP_NO_THREADS
+#endif // PIP_HAS_THREADS