Clear the cached currency keys in Currency.reset!

[lenamonj]

Currency.reset! reloads the table and clears the instance and iso_numeric caches, but not the memoized key set that Currency.new gates on. After register, a lookup, then reset!, Currency.new still admitted the removed id and raised NoMethodError from initialize_data! instead of UnknownCurrency, which find does not rescue.

reset! now clears the key set as well. The new spec fails on main and passes with the change; rspec and rubocop are clean. CHANGELOG and AUTHORS updated.

[sunny]

Thank you! \o/

[lenamonj]

The red jruby-10.0 job is the pre-existing Money::Currency#initialize is thread safe spec (currency_spec.rb:311), which pushes to a plain Array from two threads and does not call reset!. The same job is green on #1227 and on main. Could you re-run it? Happy to push an empty commit instead if that is easier.