Python coverage

Upgrading rules_python in Bazel and running tests again version 0.36.0 showed problems with coverage support.

To reproduce run `bazel test //src/test/shell/bazel:bazel_coverage_hermetic_py_test` from Bazel repository. It fails saying the test has failed, but this previously with builtin Python rules wasn't the case.

I went down the rabbit hole, but I couldn't figure it out. I think that this test should be moved out of Bazel into rules_python, if it isn't already.

在 Bazel 仓库中使用 `bazel test //src/test/shell/bazel:bazel_coverage_hermetic_py_test` 重现失败。阅读现有的 coverage 测试和 rules_python 的 coverage 支持，以确定该测试应放在这里还是 rules_python 中。完成的标准是测试归属明确，并且 coverage 行为不再报告意外失败。

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