Compiler: address PR review comments
- Define `BuiltinCallResult` type alias for the `abstract_call_builtin`
return type, replacing repeated `Pair{Any,Pair{Effects,Any}}`.
- Swap inner pair order to `Pair{Any,Effects}(exct, effects)` to follow
the `Pair{Any,Pair{Any,Effects}}` convention.
- Move `builtin_tfunction_effects` docstring from `_builtin_tfe` to the
correct function.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
