Replace references to serial interval with generation interval

[jamesmbaazam]

This PR closes #109 by:

• Renaming the serials_dist argument to gen_interval
• Revising previous wordings referring to the serial interval to use "generation interval" instead.

[sbfnk]

Yes!

I would prefer generation_interval to gen_interval. Do you think it's too much to type?

Or as a compromise we could call it generation_time (only 3 characters more than gen_interval...) which would have the benefit of being the same as in EpiNow2.

[jamesmbaazam]

Or as a compromise we could call it generation_time (only 3 characters more than gen_interval...) which would have the benefit of being the same as in EpiNow2.

I'm a big fun of {EpiNow2}, so I'll go with this. I think there is a similar notion in {epiparameter}, so +1.

Will make the change.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (6014763) 98.06% compared to head (4467fec) 98.64%.

❗ Current head 4467fec differs from pull request most recent head 8bfb2a3. Consider uploading reports for the commit 8bfb2a3 to get more accurate results

Files	Patch %	Lines
R/simulate.r	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #116      +/-   ##
==========================================
+ Coverage   98.06%   98.64%   +0.57%     
==========================================
  Files           8        8              
  Lines         518      518              
==========================================
+ Hits          508      511       +3     
+ Misses         10        7       -3     

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[sbfnk]

All looking good - we're now using both generation "time" and "interval". Perhaps that's fine as they're used interchangeably in the literature but I was wondering if it would be worth doing a search/replace "generation interval" -> "generation time" everywhere and clarify in just one point that they're the same (I made a suggestion where).