Add pytest-instafail package

[mhucka]

This adds the package pytest-instafail to the requirements for the development environment, so that we can inform people how to use the --instafail to learn about failures immediately. The built-in pytest option -x and --instafail work in complementary fashion: pytest -x makes it stop on first failure (and subsequent tests are not executed); pytest --instafail makes it print failures immediately, but continue execution.

Along with that, this PR adds more helpful test info to CONTRIBUTING.md.

[gemini-code-assist]

Code Review

This pull request updates the functional testing documentation in CONTRIBUTING.md with additional pytest options and adds the pytest-instafail dependency to the development environment files. Feedback indicates that pytest-max-compat.env.txt was compiled without the correct constraint file, leading to a noisy diff where constraint references were removed. Recompiling this requirements file with the proper constraint settings is recommended to maintain a clean change history.

[gemini-code-assist]

The compilation of pytest-max-compat.env.txt appears to have been run without the constraint file -c dev_tools/requirements/max_compat/dev.env.txt. This has resulted in a massive, noisy diff where the constraint references are removed from the # via comments of almost all packages.

Please recompile this requirements file using the correct constraint file to keep the settings functionally equivalent to the original and maintain a clean change history.

    # via
    #   -c dev_tools/requirements/max_compat/dev.env.txt
    #   tensorflow-docs

References

1. When migrating configuration, keep the settings functionally equivalent to the original to maintain a clean change history. Address known issues in the configuration in a separate change.