Reset of the timezone separator does not follow the _default_ pattern

[meduzen]

For all config methods, it’s possible to reset to the default settings by passing no parameter to it, this way you don’t have to think about it.

But setTzSeparator does not follow this pattern.

 // ✅ reset to the default value
setTimeSeparator()
setTzInRealWorldRange()
setTzConfig()

 // ❌ does not reset to the default value
setTzSeparator()

It could be considered as a bug but since it’s documented to work as it does today, it would be a breaking.

In addition, going to the default should maybe be a documented pattern.

The implementation using the Temporal API (#105) should also be adapted at the same time. In the meantime, since it’s an experimentation, it’s not needed to change it.