fix tests for when float is off (#25839)

Some tests fail when float is off but when singletons are on. This PR
makes some adjustments

1. 2 singleton tests assert float semantics so will fail.
2. the float dispatcher was being set on the server even when float was
off. while the float calls didn't do anything warnings were still
generated. Instead we provide an empty object for the dispatcher if
float is off. Longer term the dispatcher should move to formatconfig and
just reference the float methods if the flag is on
3. some external fizz runtime tests did not gate against float but
should have