[mypy]: Add type hints for EtypeResolver class:

Within rql/analyze.py:
----------------------
  add (line 403):
      if self.uid_func:
  and fix:
      error: "None" not callable  [misc]

  add (line 548):
      assert self.uid_func_mapping is not None
  and fix:
      Unsupported right operand type for in ("Optional[Dict[Any, Any]]")

  change (line 615):
      etypes = frozenset(t for t in self._nonfinal_domain if t not in etypes)
  to:
      etypes = set(t for t in self._nonfinal_domain if t not in etypes)
  and fix:
      Incompatible types in assignment (expression has type "FrozenSet[str]", variable has type "Set[Any]")


Within rql/interfaces.py:
-------------------------

Update ISchema protocol definition:
    add:
        def __contains__():
    and fix:
         error: Unsupported right operand type for in ("ISchema")  [operator]

    add:
        def rschema(self, rtype: Any):
    and fix:
        "ISchema" has no attribute "rschema"  [attr-defined]

    add:
        def eschema(self, etype: Any):
    and fix:
        "ISchema" has no attribute "eschema"  [attr-defined]

See RQL's issue: #15 (closed)