clean public header dependencies (#8725)

* remove io::ostream dependency from CString.h + clang tidy

* remove ostream.h dependency from Invocable.h

* remove Panic.h dependency from FixedCapacityVector.h

* remove ostream.h dependency from backend/ headers

* clang tidy Panic.h/Panic.cpp

libs/utils/test/test_FixedCapacityVector.cpp

@@ -17,6 +17,7 @@
 #include <gtest/gtest.h>
 
 #include <utils/FixedCapacityVector.h>
+#include <utils/Panic.h>
 
 using namespace utils;