Potential fix for code scanning alert no. 1: Use of potentially dangerous function

[Fabio3rs]

Potential fix for https://github.com/Fabio3rs/cppapiframework/security/code-scanning/1

To resolve the issue, replace the use of std::gmtime in the format function with its thread-safe variant. On platforms where gmtime_r is available (POSIX), it should be used instead; on Windows, use gmtime_s. Since we need to allocate a tm struct on the stack and pass its pointer to the respective function, this fits well. If the codebase needs to remain portable across platforms, a preprocessor check can be added to select the correct version.

Specifically:

• Edit the format function in src/PistacheCustomHttpHeaders/LastModified.hpp at lines 39-46.
• Allocate a tm tm_time struct on the stack.
• Replace std::gmtime(&cftime) with a thread-safe alternative, using gmtime_r where available and gmtime_s on MSVC/Windows.
• Pass a pointer to the local tm struct to strftime.

You may also need to include <ctime>/<time.h> and possibly include guards for platform-specific code.

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