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/piethernet.cpp

@@ -18,7 +18,7 @@
 */
 #include "piethernet.h"
 
-#ifndef PIP_NO_SOCKET
+#ifdef PIP_HAS_SOCKET
 
 #  include "piconfig.h"
 #  include "piconstchars.h"
@@ -1505,4 +1505,4 @@ bool PIEthernet::ethIsWriteable(int sock) {
 #  endif
 }
 
-#endif // PIP_NO_SOCKET
+#endif // PIP_HAS_SOCKET