More robust checks for FLOAT8E8M0

[justinchuby]

Use hasattr instead of version checks to ensure existence of the FLOAT8E8M0 type.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
3944	1	3943	4857

View the full list of 1 ❄️ flaky tests

onnxscript.converter_test.TestConverter::test_function_opset_import

Flake rate in main: 83.33% (Passed 6 times, Failed 30 times)

Stack Traces | 0.014s run time

onnxscript/converter_test.py:703: in test_function_opset_import
    @script()
     ^^^^^^^^
onnxscript/main.py:94: in transform
    result = script_check(f_ast, opset, env, src, default_opset=default_opset)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
onnxscript/main.py:38: in script_check
    return convert.translate_function_def(f)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
onnxscript/converter.py:1452: in translate_function_def
    fn_ir = self._translate_function_def_common(stmt)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
onnxscript/converter.py:1439: in _translate_function_def_common
    self._translate_stmt(s, index_of_stmt=i)
onnxscript/converter.py:966: in _translate_stmt
    return self._translate_return_stmt(node)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
onnxscript/converter.py:1089: in _translate_return_stmt
    return ret(val, 0, "")
           ^^^^^^^^^^^^^^^
onnxscript/converter.py:1065: in ret
    return_var = self._translate_expr(exp, preferred_name).name
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
onnxscript/converter.py:546: in _translate_expr
    r = self._translate_call_expr(node)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
onnxscript/converter.py:832: in _translate_call_expr
    args = autocast.static_cast_inputs(self, callee.op_schema, args)
                                             ^^^^^^^^^^^^^^^^
onnxscript/values.py:527: in op_schema
    self._op_schema = _op_schema_from_function_ir(self.function_ir, self.opset)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
onnxscript/values.py:435: in _op_schema_from_function_ir
    return onnx.defs.OpSchema(
E   ValueError: DataTypeUtils::FromDataTypeString - Received invalid data type string 'float4e2m1'.

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[justinchuby]

@gramalingam could you approve? Thanks