Make serializer dump() non-recursive

[vii]

This allows printing very deep trees without running out of stack.

[coveralls]

coverage: 100.0%. remained the same when pulling ccbafb4388288087bc4a9cd6728dec15374e353c on vii:develop into 960b763ecd144f156d05ec61f577b04107290137 on nlohmann:develop.

[vii]

Unfortunately has some compile errors on MSVC etc. Can update and fix if you like this direction -

error C7555: use of designated initializers requires at least '/std:c++20'

[t-b]

I very much like this fix here! It was on my todo list as well.

[github-actions[bot]]

This pull request has been marked as stale because it has had no activity for 30 days. While we won’t close it automatically, we encourage you to update or comment if it is still relevant. Keeping pull requests active and up-to-date helps us review and merge changes more efficiently. Thank you for your contributions!