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/pitimer.h

@@ -44,7 +44,7 @@
 
 class PIThread;
 
-#ifndef PIP_NO_THREADS
+#ifdef PIP_HAS_THREADS
 //! \~\ingroup Thread
 //! \~\brief
 //! \~english Periodic timer that emits ticks from an internal worker thread.
@@ -247,5 +247,5 @@ protected:
 	PIConditionVariable event;
 };
 
-#endif // PIP_NO_THREADS
+#endif // PIP_HAS_THREADS
 #endif // PITIMER_H