Helper templates for working specifically with std::tuple

tuple_helpers.hpp

Defines namespace tuple, containing the following templates:

• constexpr size_t tuple_size_v_omnivorous is analogous to std::tuple_size_v but accepts types with any cv and ref qualifiers.
• indexForType returns the index of type T in the given tuple; results in compilation error if type not present.
• visit implements runtime indexing of a tuple - calls a functor the value at specified index (that need not be known at compile time) as the functor's argument. The argument can be a non-const reference for a non-const tuple, so it can mutate the tuple's items.
• for_each calls a functor with each value from the tuple. Supports both const and non-const tuples. The argument can be a non-const reference for a non-const tuple, so it can mutate the tuple's items.