Document laplace_latent_solve(_tol)

[florence-bockting]

Submission Checklist

• Builds locally
• New functions marked with <<{ since 2.40 }>>
• Declare copyright holder and open-source license: see below

Summary

Document laplace_latent_solve and laplace_latent_solve_tol in the Functions Reference.
Added a new section "Return the approximate conditional mean and Cholesky factor" to embedded_laplace.qmd.
Corresponding PRs in

• math #3337
• stanc3 #1649

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): Aalto University

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC BY-ND 4.0 (https://creativecommons.org/licenses/by-nd/4.0/)

This PR used AI Assistance (Cursor).