Shellous

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- [LATERAL] Fix issue with CI action that publishes the shellous package to PyPI.

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- [API] Several API changes to the experimental `Prompt` class.
- [API] The `Result` class now has an `exit_signal` property that converts the `exit_code` value into a `Signals` enum.
- [LATERAL] Update CI settings for Python 3.12 release. Add pip --require-hashes to Github actions.
- [LATERAL] Apply security best practices to Github actions.

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- [LATERAL] Improve documentation and add security policy to the GitHub repository.
- [LATERAL] Fix two more log messages so they only appear when the SHELLOUS_DEBUG environment variable is set.
- [LATERAL] Improve reliability of CI testing on Windows.

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- [BUGFIX] Report standard error when a pipeline sub-command fails. (459)
- [LATERAL] Reduce debug logging so it only occurs when SHELLOUS_DEBUG environment variable is set.
- [LATERAL] Fix Windows CI tests for Python 3.11.5.

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- [FEATURE] Add the `coerce_arg` option in `Command` and `CmdContext`. (397)
- [BUGFIX] Improve support for built-in sequence types like `range/zip/reversed` when used as command arguments.
- [BUGFIX] Add support for using `StringIO` and `BytesIO` objects as command arguments.
- [BUGFIX] `bytearray` is now coerced to bytes when used as an argument in a Command.
- [BUGFIX] Fix subtle bug in `context_aenter/context_aexit` helpers when a re-entrant context manager overlaps in a parent/child task pair.

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- [FEATURE] Add experimental `Prompt` class for working with interactive prompts in a co-process.
- [API] The `DefaultChildWatcher` class has been downgraded to an experimental-only feature.
- [API] The `AUDIT_EVENT_SUBPROCESS_SPAWN` and `UNLAUNCHED_EXIT_CODE` constants are no longer part of the public/documented API. Internally, they were renamed.
- [LATERAL] The methods of the internal `Options` class are now deliberately marked private, as they are not part of the public/documented API.
- [LATERAL] Removed support for using Ellipsis as a special value when setting environment variables.