feat(cosmo): matter-only pedagogical cosmology - #18876

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@nstarman This is fun to see. You should make a list of pedagogical cosmologies. I will take up a few of those for PRs too. We are slowly getting there.

@preshanth I added some to #17150

Hi humans 👋 - this pull request hasn't had any new commits for approximately 4 months. I plan to close this in 30 days if the pull request doesn't have any new commits by then.

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Hi humans 👋 - this pull request hasn't had any new commits for approximately 10 months. I plan to close this in a month if the pull request doesn't have any new commits by then.

In lieu of a stalled pull request, please consider closing this and open an issue instead if a reminder is needed to revisit in the future. Maintainers may also choose to add keep-open label to keep this PR open but it is discouraged unless absolutely necessary.

If this PR still needs to be reviewed, as an author, you can rebase it to reset the clock.

If you believe I commented on this pull request incorrectly, please report this here.