Add RA for auth max_nat
As @tchajed pointed out, this RA is quite commonly used. While porting developments as a consequence of !461 (merged) I noticed it's also used in ReLoC.
So, concretely, there are the following uses:
- Iris: https://gitlab.mpi-sws.org/iris/iris/-/blob/master/theories/heap_lang/lib/counter.v#L16
- ReLoC: https://gitlab.mpi-sws.org/iris/reloc/-/blob/7dca8f9472290626ac5174d5789512234ce115e9/theories/examples/symbol.v#L49
- Perennial: https://github.com/mit-pdos/perennial/blob/master/src/algebra/fmcounter.v
Would be good to add it to algebra/lib
so people don't reprove the same stuff all the time.