Turn on IRModule mutation detector in tests by default

[areusch]

In #11372, @gigiblender created a utility that detects if an IRModule modifies any of the visitable attributes of an IRModule in-place. This issue tracks implementing that utility as the default in all Python tests. Here are the steps:

• Determine what kind of switch we should use for this. In the original PR, a switch was created using PassContext. We should find a way to modify the value of the switch for all tests via a pytest fixture.
• Add such pytest fixture to the codebase and determine which tests are failing, if any.
• Turn on the fixture for tests that aren't currently failing, and list the tests which need to be fixed here.
• Fix remaining tests as a community.

@mikepapadim is going to take a look at this.

[mikepapadim]

I 've been looking into fixtures and #11498. If we don't want to expose the switch on the python side, one way might be to keep the switch into PassContext and expose an env variable to enable it. Then, we could use a session scoped
fixture to enable it.

[areusch]

i was thinking to do something kind of like this but rather put the variable in tvm.testing as a global var rather than environment var, and use mock.patch in a pytest fixture to set it. what do you think about that?