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.cpp

@@ -16,7 +16,7 @@
     You should have received a copy of the GNU Lesser General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
-#ifndef PIP_NO_FILESYSTEM
+#ifdef PIP_HAS_FILESYSTEM
 #include "pidir.h"
 
 #include "piincludes_p.h"
@@ -612,4 +612,4 @@ void PIDir::CurrentDirOverrider::save(const PIFile::FileInfo & info) {
 	else
 		PIDir::setCurrent(PIDir::current().path() + PIDir::separator + p);
 }
-#endif // PIP_NO_FILESYSTEM
+#endif // PIP_HAS_FILESYSTEM