deprecate `stage` in cocotb tests/RegressionManager

[ktbarrett]

This feature existed to order tests logically into stages: tests from earlier stages are run before tests from later stages. But no additionally functionality wrt to this was added. Did a regression pass a stage? What does it mean if anything for it to pass a stage? Why can't the user just reorder tests lexically? Why does test order matter? Shouldn't they be independent?

I've also never seen it used in the wild.

So, I feel this should be deprecated without an alternative and removed in 3.0.

[cmarqu]

FWIW, this came in via https://github.com/cocotb/cocotb/commit/a465523e6197b096b41e281cae6256dd61e9b997

[ktbarrett]

This can be used to ease the analysis of output files or the test outputs.

Any idea what's meant by this?

[cmarqu]

Ping @wallento