gh-152548: Convert the test_signal wakeup tests to @runInSubprocess()

[serhiy-storchaka]

The wakeup tests in WakeupSignalTests and WakeupSocketSignalTests need a process with no background thread so that signals are delivered to the main thread. Each was driven as a hand-written script string run in a child process via assert_python_ok('-c', ...), signalling failures with bare raise and reported to the runner only through the child exit code.

With @isolation.runInSubprocess() the same code runs as a normal method body in a fresh subprocess, using self.assert* and reported per test, with the subprocess traceback shown as the cause of a failure. The check_wakeup() helper becomes an ordinary helper that runs a test(read) callback in-process and asserts the read-back; the _testcapi skips move to the parent process (so no subprocess is spawned when skipped).

• Issue: Add a decorator to run a test in an isolated subprocess #152548

[read-the-docs-community]

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± library/test.html
± whatsnew/changelog.html