PERF: fastpaths in tzconversion
Should address some asv regressions that happened between 1.4.0 and 1.5.0
Which ones in particular improved? i dont have them on hand, but my recollection is it was tslibs-specific asvs and it was utc cases and empty cases, both of which had gone from super-fast to just-fast Thanks @jbrockmendel 