Triple Arena

Provides very flexible arena type Arena<T, P> and pointer type Ptr. The arena supports non-Clone T, optional generation counters (zero-cost when omitted), and zero-cost arena differentiation. The generic P in P is a marker that can be used to guard against using the wrong Ptr in the wrong Arena when multiple Arenas are in use. The P can optionally include a generation number, in which the arena will use a generation counter to prevent invalidated pointers from working.

No unsafe is used. no_std compatible.