6140fd9 causes a binary size regression in conhost.
This PR fixes most if not all of the regression, by replacing `FMT_STRING`
with `FMT_COMPILE` allowing us to drop most of the formatters built
into fmt during linking (for instance floating point formatters).
Additionally `std::wstring` was replaced with `fmt::basic_memory_buffer`
in the same vein as was done for VtEngine. Stack is
cheap and this prevents any unnecessary allocations.
## PR Checklist
* [x] I work here
* [x] Tests added/passed
## Validation Steps Performed
* vttest 11.2.5.3.6.7 and .8 (DECSTBM and SGR) complete successfully ✅
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