fix: `assert` object library uses `spdlog::spdlog` instead of `fmt::fmt`

[rroelke]

Resolves #5534 which points out that use of fmt::fmt brings in an additional dependency which may conflict with spdlog::spdlog.

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TYPE: NO_HISTORY DESC: assert object library uses spdlog::spdlog instead of fmt::fmt

[OgreTransporter]

I have completely removed spdlog and fmt as external dependencies. The code probably still needs to be improved. Suggestions are welcome. #5537