Remove pmc dependency

[navidmahmoudian]

Introduce WITH_PMC CMake option to conditionally disable the PMC dependency, aligning with the MIT license. This change also resolves compilation issues on Windows with the MSVC compiler.

[navidmahmoudian]

For more details, please see the response this issue.

[jingnanshi]

Thanks for the PR. Since PMC is downloaded during build so no need to remove the dependency for licensing issue. In other words, because we don't include PMC source code with our repo, GPL license is not an issue. I'll look at the MSVC compilation issue when I have time.

[navidmahmoudian]

Hello,

Thanks for your reply. I've addressed the MSVC issue in my PR by using std::atomic within pkc.cpp. The unit tests are currently passing. Would you mind taking a look when you have a moment, or perhaps trying to compile and run the tests on your end?