Make a deep copy of the returned value from setlocale

[victorshcherbakov]

When I tested this library on Linux Manjaro 6.6.85 with enabled ASAN I faced with the issue heep-use-after-free.

As I understood it's necessary to make a deep copy of the returned value from setlocale, because during the next call of this function, the returned memory can be freed.
Also https://en.cppreference.com/w/cpp/locale/setlocale recommends making a deep copy.
When I looked at the setlocale implementation in glibc 2.41 (it's a version from my system) I see that there is a chance of such behaviour (a returned memory can be freed):
https://github.com/bminor/glibc/blob/release/2.41/master/locale/setlocale.c#L395
I made such a fix and now everything is OK.

My compiler is clang 19.1.7.

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[victorshcherbakov]

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[damyanp]

Related #7506

[damyanp]

We think that #7506 supercedes this one. We should double check that this is the case, but for now we'll close this PR.