added a write-up of creating a simple sender

[dietmarkuehl]

No description provided.

[Copilot]

Pull request overview

Adds a new tutorial/example demonstrating how to implement a custom sender (pop_sender) for an asynchronous_stack, along with a detailed documentation write-up and CMake integration so the example builds with the existing examples suite.

Changes:

• Added examples/tutorial-create-a-sender.cpp implementing a pop_sender with stop support and a demo main().
• Registered the new example target in examples/CMakeLists.txt.
• Added docs/create-a-sender.md explaining sender construction step-by-step using the asynchronous stack example.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 8 comments.

File	Description
examples/tutorial-create-a-sender.cpp	New example sender implementation + demo program for popping/pushing and stop behavior.
examples/CMakeLists.txt	Adds the new tutorial example to the examples build list.
docs/create-a-sender.md	New tutorial document explaining the sender/operation-state pattern and stop callbacks.

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[coveralls]

coverage: 95.062% (+0.004%) from 95.058% — doc-create-a-sender into main