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/io_devices/pidir.h

@@ -30,7 +30,7 @@
 #include "piregularexpression.h"
 
 
-#ifndef PIP_NO_FILESYSTEM
+#ifdef PIP_HAS_FILESYSTEM
 //! \~\ingroup IO
 //! \~\brief
 //! \~english Local directory.
@@ -218,10 +218,10 @@ private:
 
 	PIString path_, scan_;
 };
-#endif // PIP_NO_FILESYSTEM
+#endif // PIP_HAS_FILESYSTEM
 
 
-#ifndef PIP_NO_FILESYSTEM
+#ifdef PIP_HAS_FILESYSTEM
 inline bool operator<(const PIFile::FileInfo & v0, const PIFile::FileInfo & v1) {
 	return (v0.path < v1.path);
 }
@@ -245,7 +245,7 @@ inline PICout operator<<(PICout s, const PIDir & v) {
 	s.restoreControls();
 	return s;
 }
-#endif // PIP_NO_FILESYSTEM
+#endif // PIP_HAS_FILESYSTEM
 
 
 #endif // PIDIR_H