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_utils/pifiletransfer.cpp

@@ -19,7 +19,7 @@
 
 #include "pifiletransfer.h"
 
-#ifndef PIP_NO_FILESYSTEM
+#ifdef PIP_HAS_FILESYSTEM
 const char PIFileTransfer::sign[] = {'P', 'F', 'T'};
 
 PIFileTransfer::PIFileTransfer() {
@@ -341,4 +341,4 @@ void PIFileTransfer::send_finished(bool ok) {
 	}
 }
 
-#endif // PIP_NO_FILESYSTEM
+#endif // PIP_HAS_FILESYSTEM