* env: adds --ignore-signal
This commit implement #6164.
* env: handle STOP signal and fix styling issue
* env: fix encoded bytes
* env: adds SAFETY comment and handle special signals in ignore_signal
* env: fix parsing to have compatible behaviour
* env: remove derive from Options
* env: changed safety comment, handle duplications after parsing and non-unix cfg
* env: adds tests for ignore-signal parsing and invalid and special signals
* env: change signal values to be non-constant
* env: adds testing for signal ignoring
* env: styling and remove unix specific derive
* test_env: add SIGSTOP to cspell workspace wordlist
* env: makes signal handling unix specific
* env: make ignore-signal function invocation unix specific
* test_env: make signal vector use slices ref instead of vec (linter)
* env: makes ignore-signal in options unix specific
* test_env: add unix specific import
Summary of changes in UCommand:
* Extend UCommand by builder methods and simplify methods in TestScenario
* Simplify code structures where possible. Add documentation.
* Store bin_path as PathBuf and util_name as String in all structs
* Remove UCommand::util and make bin_path, temp_dir private
* Rename UCommand::with_limit -> UCommand::limit
Summary of changes in TestScenario:
* Rename some parameters in TestScenario methods to be more descriptive
* Remove ucmd_keepenv, cmd_keepenv from TestScenario. Use UCommand::keep_env instead.
