fix: fix cgo memory leak

Author: Rouzip

perf/collector_libpfm.go

@@ -266,10 +266,12 @@ func readPerfEventAttr(name string, pfmGetOsEventEncoding func(string, unsafe.Po
 func pfmGetOsEventEncoding(name string, perfEventAttrMemory unsafe.Pointer) error {
 	event := pfmPerfEncodeArgT{}
 	fstr := C.CString("")
+	defer C.free(unsafe.Pointer(fstr))
 	event.fstr = unsafe.Pointer(fstr)
 	event.attr = perfEventAttrMemory
 	event.size = C.ulong(unsafe.Sizeof(event))
 	cSafeName := C.CString(name)
+	defer C.free(unsafe.Pointer(cSafeName))
 	pErr := C.pfm_get_os_event_encoding(cSafeName, C.PFM_PLM0|C.PFM_PLM3, C.PFM_OS_PERF_EVENT, unsafe.Pointer(&event))
 	if pErr != C.PFM_SUCCESS {
 		return fmt.Errorf("unable to transform event name %s to perf_event_attr: %d", name, int(pErr))