factored the optional_sender into a header shared by multiple tests

[dietmarkuehl]

No description provided.

[Copilot]

Pull request overview

This PR factors a locally-defined optional_sender test helper out of individual tests into a shared header so multiple tests can reuse the same sender implementation.

Changes:

• Added a shared test helper header: test/optional_sender.hpp.
• Updated exec-stopped-as-optional and exec-stopped-as-error tests to include and use test::optional_sender.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
tests/beman/execution/include/test/optional_sender.hpp	Introduces shared optional_sender sender type for reuse across tests.
tests/beman/execution/exec-stopped-as-optional.test.cpp	Replaces local helper with the shared test::optional_sender header.
tests/beman/execution/exec-stopped-as-error.test.cpp	Replaces local helper with the shared test::optional_sender header.

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[coveralls]

coverage: 95.238%. remained the same
when pulling 507b19e on factor-out-optional_sender
into 82f2c42 on main.