clang warnings in osciallator miniapp

clang reports use of static member variable that has not been initialized. here is a prototypical instance

In file included from /Users/bloring/sensei/miniapps/oscillators/oscillator.cpp:4:
/Users/bloring/sensei/miniapps/oscillators/include/format.h:589:25: warning: instantiation of variable 'fmt::internal::BasicData<void>::POWERS_OF_10_64' required here, but no definition is available [-Wundefined-var-template]
  return t - (n < Data::POWERS_OF_10_64[t]) + 1;
                        ^
/Users/bloring/sensei/miniapps/oscillators/include/format.h:568:25: note: forward declaration of template entity is here
  static const uint64_t POWERS_OF_10_64[];
                        ^
/Users/bloring/sensei/miniapps/oscillators/include/format.h:589:25: note: add an explicit instantiation declaration to suppress this warning if 'fmt::internal::BasicData<void>::POWERS_OF_10_64' is explicitly instantiated in another translation unit
  return t - (n < Data::POWERS_OF_10_64[t]) + 1;
                        ^

here is the class in question

 563 // Static data is placed in this class template to allow header-only
 564 // configuration.
 565 template <typename T = void>
 566 struct BasicData {
 567   static const uint32_t POWERS_OF_10_32[];
 568   static const uint64_t POWERS_OF_10_64[];
 569   static const char DIGITS[];
 570 };