gh-268: including CMB lensing

[raphkou]

🚀 Pull Request Checklist

✅ Summary

This PR allows computing CMB lensing power spectrum and cross-correlations with position and shear tracers.

🔄 Changes

• I added a new observable cmb.py which allows computing CMB lensing window function.
• I modified angular_two_point.py to compute CMB lensing power spectrum and cross-correlations. In particular, I modified the variable C_ell_out to handle the case where the tracers have different numbers of bins. This is the case of CMB lensing, which has only one redshift bin.
• I modified several cosmology files (camb, class, jax) to compute z_star which is required to compute the CMB lensing window function.
• I added a few unit tests in test_cmb.py, allowing to check the computation of the CMB lensing window function, power spectrum, and cross-correlations.

🛠 How to Test

I added the notebook cmb.ipynb in the playground (see PR cloe-org/playground#116), which shows how to compute the CMB lensing power spectrum and cross-correlations, and performs a benchmark against CAMB and CCL.

📝 Documentation

• This PR updates documentation

🏗 Related Issues

Resolves #268.

📌 Additional Notes

Pseudo-cl computation not implemented yet.

---

✅ PR Checklist for Developers

• I have titled this PR before merging as "gh-#:", where "#" represents the task it closes
• I have run locally pre-commit using pre-commit run --all-files
• I have tested my changes locally
• No new warnings or errors introduced
• I have updated documentation (if applicable)
• My changes do not introduce breaking changes (i.e: the package still gets installed)
• I have added unit tests (if applicable)
• I have consistently updated the GitHub information for the project, including milestones, task types, and other relevant details.

✅ PR Checklist for Reviewers

• The next PR targets the correct branch
• CI tests have run and passed for the latest commit on the source branch
• Check that the code can still be installed if new packages are imported
• If necessary, the notebooks in the playground will be updated in a corresponding follow-up PR
• Coverage percentage is retained or increased
• Quality of new/changed code is acceptable
• Quality of new/changed unit tests is acceptable
• No data files have been included in the commits
• Implementation follows the agreed task description point by point
• Check that any added folder/file has been added to the README.md file
• Check that the documentation has been updated accordantly
• Check that the corresponding branch has been deleted after merging. If not, delete it

[arthurmloureiro]

Excellent stuff @raphkou !

Just a few questions and comments!

[gcanasherrera]

Hey @raphkou , I was reviewing this more in detail, and I guess it is fine the way that it is, but, could we please update the docs and make sure that we are compatible with numpy>2 before merging? Thanks

[raphkou]

Hi @gcanasherrera, thanks for reviewing this PR. I have updated the code so that it is indeed compatible with numpy>2. It seems to be alright now.

[gcanasherrera]

For Guada to remember: this is being well taken care of, just on hold due to holidays.

[gcanasherrera]

Many thanks @raphkou

[gcanasherrera]

@all-contributors please add @raphkou for code, ideas, docs

[allcontributors]

@gcanasherrera

I've put up a pull request to add @raphkou! 🎉