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/system/piprocess.h

@@ -26,7 +26,7 @@
 #ifndef PIPROCESS_H
 #define PIPROCESS_H
 
-#ifndef PIP_NO_PROCESS
+#ifdef PIP_HAS_PROCESS
 
 #  include "pithread.h"
 
@@ -258,5 +258,5 @@ private:
 	std::atomic_bool exec_finished;
 };
 
-#endif // PIP_NO_PROCESS
+#endif // PIP_HAS_PROCESS
 #endif // PIPROCESS_H