Updates s3 construction to be closer to best practice

[seabbs]

As the title this updates epidist_linelist, epidist_direct_model, and epidist_latent_individual to be closer to the structures used in scoringutils and elsewhere. Note it also standarises entry points across models and adds a new low level default method for epidist linelist that can be used directly with simulated data.

It also adds a first pass at a sensible user interface for linelist data and renames both linelist and models in line with #433

[codecov]

Codecov Report

Attention: Patch coverage is 83.89831% with 19 lines in your changes missing coverage. Please review.

Project coverage is 91.20%. Comparing base (d02c7c7) to head (0ccc524).
Report is 51 commits behind head on main.

Files with missing lines	Patch %	Lines
R/linelist_data.R	78.37%	16 Missing ⚠️
R/utils.R	70.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #441      +/-   ##
==========================================
+ Coverage   88.55%   91.20%   +2.64%     
==========================================
  Files          11       16       +5     
  Lines         402      466      +64     
==========================================
+ Hits          356      425      +69     
+ Misses         46       41       -5     

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