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/pimutex.h

@@ -28,7 +28,7 @@
 
 #include "piinit.h"
 
-#ifndef PIP_NO_THREADS
+#ifdef PIP_HAS_THREADS
 //! \~\ingroup Thread
 //! \~\brief
 //! \~english Mutex for mutual exclusion between threads.
@@ -94,9 +94,9 @@ private:
 	bool cond;
 };
 
-#endif // PIP_NO_THREADS
+#endif // PIP_HAS_THREADS
 
-#ifdef PIP_NO_THREADS
+#ifndef PIP_HAS_THREADS
 //! \~\ingroup Thread
 //! \~\brief
 //! \~english Dummy mutex for builds without threading support.
@@ -117,6 +117,6 @@ class PIMutexLocker {
 public:
 	PIMutexLocker(PIMutex &, bool = true) {}
 };
-#endif // PIP_NO_THREADS
+#endif // PIP_HAS_THREADS
 
 #endif // PIMUTEX_H