Issue 51: First pass at broadcasting

[seabbs]

This PR partly resolves #51 by introducing a broadcasting approach to EpiLatentModels which can be used both for day of the week models and for piecewise constant latent models.

Depending on how we feel about this approach we may want to abstract some of this into its own module at some point to allow broadcasting in other parts of the code base.

It does not add the ascertainment EpiObsModel or Random EpiLatentModel which will be needed to full address #51.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 79.06977% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 95.43%. Comparing base (401e028) to head (cbcd087).

Files	Patch %	Lines
EpiAware/src/EpiAwareBase/functions.jl	0.00%	4 Missing ⚠️
EpiAware/src/EpiAwareBase/generate_models.jl	66.66%	3 Missing ⚠️
...Aware/src/EpiLatentModels/broadcast/latentmodel.jl	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #171      +/-   ##
==========================================
- Coverage   97.99%   95.43%   -2.56%     
==========================================
  Files          28       32       +4     
  Lines         249      285      +36     
==========================================
+ Hits          244      272      +28     
- Misses          5       13       +8     

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[seabbs]

Coverage is a bit low so I will address that but I think this is still good to review as is.

[SamuelBrand1]

I like this approach, nice and flexible.

[seabbs]

I think this addresses the coverage gaps and includes your suggestions.