fix: tighten up shell escaping to handle some edge cases

[braindigitalis]

When passing command line parameters to a bourne style shell using dpp::utility::exec(), the user could be misled to believe DPP does escaping of ` symbols, $(), etc (it did not).

This PR adds support for escaping that properly blocks those bourne behaviours in Linux and other similar operating systems, so that it is a bit more friendly.

Note, this does not absolve the library user of NOT passing user crafted data into dpp::utility::exec(). It is not our job to protect the library users from stupidity.

Windows doesn't need this patch, as std::quoted() will suffice there.

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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[Neko-Life]

lgmt