General Issue: Restructure Files for ADEG and ADVS Parameters

[bundfussr]

Background Information

The files derive_adeg_parms.R and derive_advs_parms.R should be restructured such that there is one file per "parameter". E.g., derive_param_qtc.R contains derive_param_qtc() and compute_qtc().
The test files should be restructured accordingly.

Definition of Done

derive_adeg_parms.R and derive_advs_parms.R and their test files are replaced.

[bms63]

@pharmaverse/admiral @pharmaverse/admiral_comm great issue to dig into the files of admiral and get familiar with some some of the functions. This is probably 1 hour of work and might produce some "uuummmm...moments" that we will need to discuss in the Pull Request.