PoC: add pytest dlt package with useful helpers

[sh-rp]

Description

We have a bunch of very useful testing helpers which we would like to share as a separate package to pypi. This PR servers as a starting point to discuss the repository structure with this package. For testing, one single util function is moved to the new package.

Things to decide (with initial suggestions)

• The name of the test package (pytest-dlt)
• The versioning and release scheme (1-1 with the main dlt package, we always have the exact same version and release at the same time)
• License (same as dlt package)
• Location of package (see current repo, it is in a folder and included in the main workspace via the uv sources section)
• Folder / module structure within this new test package (no proposals yet)

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[zilto]

Awesome feature (eager to use it myself). Regarding naming, the convention suggests dlt-pytest instead of pytest-dlt (see results for "pytest" on pypi)

[sh-rp]

Awesome feature (eager to use it myself). Regarding naming, the convention suggests dlt-pytest instead of pytest-dlt (see results for "pytest" on pypi)

chat-gpt says the convention is pytest first, but I am not sure that that is true. dlt-pytest sounds nicer to me too.

[zilto]

I might have been wrong though. This pytest docs page lists a lot of pytest-PROJECT_NAME plugins.

Though, if the number of dlt related projects grow, it can be useful to keep track of them using the dlt- prefix.

I'm ok with either