Prepare 0.3.13 CRAN release

[danielinteractive]

• [x] Add ORCID ID
• [x] Upgrade lifecycle label from experimental to stable for most functions
• [x] Add my company to funders
• [x] clean up meanwhile unnecessary imports
• [x] Check on R-Hub
• [x] Clean NEWS
• [x] bump version
• [x] Fix any CRAN reports:
  • [x] tern.mmrm has one test failing

     Error ('test-lsmeans.R:190:3'): h_get_average_visit_specs uses number of patients with any of the averaged visits as n
     Error in `refit_multiple_optimizers(fit = fit, control = control)`: No optimizer led to a successful model fit. Please try to 
     use a different covariance structure or other covariates.

    addressed in https://github.com/insightsengineering/tern.mmrm/pull/191

[danielinteractive]

First version submitted now

[danielinteractive]

Submitted again now that tern.mmrm test has been fixed on CRAN

[danielinteractive]

package mmrm_0.3.13.tar.gz is on its way to CRAN.