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/piconditionvar.cpp

@@ -23,7 +23,7 @@
 #  define _WIN32_WINNT 0x0600
 #endif
 
-#ifndef PIP_NO_THREADS
+#ifdef PIP_HAS_THREADS
 #include "piconditionvar.h"
 #include "piincludes_p.h"
 #ifdef WINDOWS
@@ -178,4 +178,4 @@ void PIConditionVariable::notifyAll() {
 	pthread_cond_broadcast(&PRIVATE->nativeHandle);
 #endif
 }
-#endif // PIP_NO_THREADS
+#endif // PIP_HAS_THREADS