Fix CachedMapper's rec/rec_function_definition typing

[majosm]

Eliminates the basedpyright warnings that appear every time a cached mapper overrides rec/rec_function_definition, e.g.:

pytato/transform/__init__.py:529:44 - warning: Type of "rec" is partially unknown
  Type of "rec" is "(self: Mapper[Unknown, Unknown, ...], expr: Array | AbstractResultWithNamedArrays, ...) -> Unknown" (reportUnknownMemberType)
pytato/transform/__init__.py:529:44 - warning: Argument type is unknown
  Argument corresponds to parameter "result" in function "_cache_add" (reportUnknownArgumentType)
pytato/transform/__init__.py:542:25 - warning: Type of "rec_function_definition" is partially unknown
  Type of "rec_function_definition" is "(self: Mapper[Unknown, Unknown, ...], expr: FunctionDefinition, ...) -> Unknown" (reportUnknownMemberType)
pytato/transform/__init__.py:542:25 - warning: Argument type is unknown
  Argument corresponds to parameter "result" in function "_function_cache_add" (reportUnknownArgumentType)

by using super(CachedMapper, self) instead of Mapper.

Testing out Claude for type checking troubleshooting. 🙂 cc @lukeolson