Exit limit as an input

[ngomezve]

Addresses issue #60.

A new input exit_limit is required that defines the aircraft's exit limit and therefore the maximum number of passengers that can sit in the cabin. The maximum payload is still determined through max_pax, but a comment has been added to explain that this is an equivalent number of passengers.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 5.29%. Comparing base (31a239c) to head (c50496a). Report is 131 commits behind head on main.

Files with missing lines	Patch %	Lines
src/structures/update_fuse.jl	0.00%	3 Missing :warning:
src/IO/read_input.jl	50.00%	1 Missing :warning:

:exclamation: There is a different number of reports uploaded between BASE (31a239c) and HEAD (c50496a). Click for more details.

HEAD has 2 uploads less than BASE

| Flag | BASE (31a239c) | HEAD (c50496a) | |------|------|------| ||3|1|

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #63 +/- ## ========================================== - Coverage 77.77% 5.29% -72.48% ========================================== Files 71 71 Lines 13536 13416 -120 ========================================== - Hits 10528 711 -9817 - Misses 3008 12705 +9697 ```

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[ngomezve]

Closing as long outdated.