[Describe your pull request here. Please read the text below the line and make sure you follow the checklist.]

This pull request restores some missing symbols that were present in the <nlohmann/json.hpp> header, but weren't exported in json.cppm. These include specialisations in namespace std (such as hash<> and less<>), as well as nlohmann::literals::json_literals::*. This is necessary as without this those specialisations and symbols are inaccessible from the module.

• The changes are described in detail, both the what and why.
• If applicable, an existing issue is referenced.
• The Code coverage remained at 100%. A test case for every new line of code.
• If applicable, the documentation is updated.
• The source code is amalgamated by running make amalgamate.