Fix cli11 cstdint

[kanakaero]

Proposed Changes

Add a missing include to the vendored CLI11 header.

GCC 14+ no longer permits transitive inclusion of fixed-width integer types. CLI11.hpp uses uint64_t without including <cstdint>, which causes build failures with GCC 15.

Related Work

None

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[pcarruscag]

Thanks for the fix.
We should try to use the current version of CLI11 and integrate it as a submodule like we do with other github-based dependencies. If you are looking for simple things to do in SU2, this would be one.

[kanakaero]

Yeah, that would be a better long term approach, I will look into it.