[Unity][TVMScript] Avoid dangling reference when printing Call attrs

[Lunderberg]

Prior to this commit, the tvm::script::printer::AttrPrinter class took the attribute path as a const ObjectPath&. In both places where an AttrPrinter is called, the temporary object n_p->Attr("attrs") is passed for this argument. While binding a temporary object to a const reference can extend the lifetime of the temporary, this requires the const reference to be in the same scope as the temporary, and does not apply in this case (see this stackoverflow post). Therefore, this reference is only valid through the construction of AttrPrinter printer, and is invalid during its usage on the following line.

This dangling reference has caused segfaults in CI for unrelated changes (example), and can be reproduced with the following test case.

import pytest

from tvm.script import relax as R

@pytest.mark.parametrize("iter", range(10000))
def test_argmax_without_specified_axis(iter):
    @R.function
    def func(x: R.Tensor((1, 2, 3, 4), "float32")):
        return R.argmax(x)

    func.script(show_meta=True)

This test case is not included in this commit, as the reproduction is not consistent, with failure requiring on the order of 10k iterations to trigger. In addition, reproduction was sensitive to the following conditions.

• The function being printed must contain at least one relax::Call node, with an operation that has attributes.

• TVM must be built with optimization enabled. In gcc, the -ftree-dse optimization, which is part of -O1, is required to trigger the bug.

• Python's default allocation must be used. If PYTHONMALLOC=malloc is set to instead use the system's malloc, the segfault was no longer triggered.

This commit updates AttrPrinter to accept the ObjectPath by value. With the change applied, the above test ran 100k times without error.