Fix duplicate __guard macro definition in set/procedures.inc

[Copilot]

Addresses feedback from PR #269: set/procedures.inc still had two __guard definitions that could trigger redefinition warnings in nested template instantiations.

Changes

• Removed unconditional #define __guard __set_guard before includes
• Repositioned conditional undef/define block between copy_set_T_to_internal_T.inc and define_derived_macros.inc
• Now matches the pattern used in vector, deque, ptr, queue, and stack templates

Before

#define __guard __set_guard
#include "parameters/T/copy_set_T_to_internal_T.inc"
#include "parameters/T/define_derived_macros.inc"

#if (defined(__guard))
#  undef __guard
#endif
#define __guard __set_guard

After

#include "parameters/T/copy_set_T_to_internal_T.inc"
#if (defined(__guard))
#  undef __guard
#endif
#define __guard __set_guard
#include "parameters/T/define_derived_macros.inc"

The macro is now defined exactly once with conditional undef protection, eliminating redefinition warnings.

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