Distinction between max payload and max pax

[ngomezve]

This PR is a revived form of PR #63. It introduces the exit_limit as a way to specify the maximum number of seats in the cabin. This is stored as a field in fuselage.cabin. In addition, the name of the input max_pax is changed to the more accurate max_payload_in_pax_equivalent.

The code now uses the exit limit to resize the fuselage where appropriate. The PR also fixes a very minor bug in the double-decker case (a parg parameter had been left behind).

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 35.48387% with 20 lines in your changes missing coverage. Please review.

Project coverage is 73.19%. Comparing base (430cfd8) to head (6499311).
Report is 27 commits behind head on main.

Files with missing lines	Patch %	Lines
src/structures/size_cabin.jl	0.00%	9 Missing ⚠️
src/structures/update_fuse.jl	22.22%	7 Missing ⚠️
src/IO/read_input.jl	75.00%	2 Missing ⚠️
src/IO/save_model.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
- Coverage   73.41%   73.19%   -0.23%     
==========================================
  Files          77       80       +3     
  Lines       13908    13459     -449     
==========================================
- Hits        10211     9851     -360     
+ Misses       3697     3608      -89     

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[argonaut22]

@ngomezve, just finished reviewing. left brief notes in the [Merge branch 'main' into dev_cargo_ref](2e87f30) commit instead of this thread by accident 🤦. overall, looks good

[ngomezve]

Thanks @argonaut22. Unfortunately, it seems like you reviewed the diffs in a merge commit from main, instead of the overall diffs in the PR! In essence, commit (2e87f30) contains diffs from older PRs already in TASOPT that I was merging into this branch to resolve merge conflicts. Could you please review the actual changes in this PR? You can do it by going to the "Files changed" tab. It should be very short as I didn't add a lot of code.