Add a way to use dioxus-i18n in tests

[breard-r]

Hello,

Currently, it seems impossible to use dioxus-i18n in tests. Trying to use use_init_i18n in a test function results in a panic with the following message:

to be in a dioxus runtime

Not initializing it obviously fails too.

It would be nice to have a way to test the translations.

Example use case: An internationalized Dioxus app that need to display an unsigned integer in letters and therefore need to test that, for each supported language, the algorithm converts the integer into the correct words.