new: test: Regex support for logs and cmd output in pytest

Improve and unify the handling of regular expressions when searching in logs, files and command output in system tests.
- Use `Re()` for constructing regular expressions, which is an imported shorthand for `re.compile()` (imported as `from re import compile as Re`
- Add new `isctest.text.Text` interface which is a text wrapper that supports the `in` operator for line matching operation for both strings and regular expressions, e.g.:
  - `assert "running" in ns1.log`
  - `assert Re("a.example..*10.0.0.1") in response.out`
- Use the new `isctest.text.Text` for:
  - `isctest.run.cmd()` output, where `.out` and `.err` can be used for stdout and stderr contents
  - `NamedInstance.log` rather than the previous log interface (`.expect()` and `.prohibit()` is no longer available or needed. The `in` operator along with an `assert` statement can be used now instead.)
  - `NamedInstance.rndc()` output, which returns identical output as `isctest.run.cmd()`

Merge branch 'nicki/pytest-grep' into 'main'

See merge request isc-projects/bind9!11054