Nim 2.2 comes with compile-time string formatting that doesn't raise
exceptions if the format string is invalid - instead a compile-time
error is given.
This PR introduces a backport of that feature which improves performance
and reduces the risk that formatting causes the app to crash and will
help migrating the codebase to newer nim versions that track exceptions
more carefully.
There should be no change in runtime behavior (except formatting being a
bit faster)
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