Look for uses of `pyrsistent.Map` where no updates occur, replace with `immutables.Map`

[inducer]

x-ref: https://gist.github.com/1st1/292e3f0bbe43bd65ff3256f80aa2637d?permalink_comment_id=2399355 x-ref: https://github.com/inducer/pytato/pull/277#discussion_r837867347 x-ref: https://github.com/inducer/pytato/issues/303

cc @kaushikcfd