refactor(async): Modernize coroutine helpers and add follow_up functions

[Feinq]

Summary

This is a refactoring and stability improvement for the coroutine helper functions on message_create_t and interaction_create_t.

Following a review discussion, all relevant co_ helpers have been updated to use the modern "pass-by-value and move" C++ idiom. This change achieves two primary goals:

1. It fixes a critical dangling reference bug present in the original implementations that could lead to use-after-free errors and crashes.
2. It simplifies the API by replacing redundant const& and && overloads with a single, more efficient signature.

To support this refactoring, interaction_modal_response was also made fully copyable and movable by implementing the Rule of 5.

While the Rule of 0 would be preferred, this was not possible due to the class's explicitly declared virtual destructor.

This PR also introduces the follow_up function as originally intended and includes several other minor improvements discovered during implementation.

Changes

• Refactoring & Bug Fix:
  • Refactored all co_ helpers (co_reply, co_send, co_edit_response, etc.) to take parameters by value. This corrects a systemic dangling reference bug and modernizes the API.
  • Explicitly defaulted the Rule of 5 (copy/move constructors and assignment operators) for interaction_modal_response to make it a properly movable type, enabling its use with the new pass-by-value pattern.
• New Feature:
  • Added follow_up and co_follow_up functions to interaction_create_t.
• Other Improvements:
  • API Consistency: Added a co_edit_original_response overload that accepts a std::string for better consistency with similar functions.
  • Performance: The for-loop in edit_original_response now uses const& to avoid unnecessary copies of file data.
• Documentation: Corrected several doxygen comments that incorrectly referred to "slash commands" instead of the more general "interactions."

Testing

All changes were thoroughly tested with a local bot, covering both lvalue (copy) and rvalue (move) call patterns for all refactored functions to ensure correctness and prevent regressions.

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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[Mishura4]

At this point the right thing to do with these co_ functions would be to pass by value and then move in the lambda capture. With that said that'll require a lot of changes to the PHP script so, I think we should accept this PR for now, but if you want to have a shot at the PHP script to do that, feel free to

[Feinq]

The PR description has been updated.

On a related note, I've noticed that this refactoring will make the LNK2019 error example in the troubleshooting documentation obsolete, as the mangled name for co_reply will change. See here.
Since I'm developing on Linux, I'm unable to generate the updated MSVC linker error to replace it.

Suggestions would be appreciated on this.