Homogeneous model of cryogenic tanks

[ngomezve]

This PR introduces a homogeneous model for a cryogenic tank. This treats the fluid inside the tank as a mixture of a saturated liquid and a saturated vapor. Through this, TASOPT can model the evolution of pressure in time inside the tank, as well as calculate the required venting more accurately. In addition, this PR also:

• Introduces a new CryoTank module, which is where the homogeneous model is stored.
• Changes the way that venting is treated in mission; now venting is only added at the end of the flight profile. Note that this results in a slightly inaccurate profile.
• Adds a natural convection model to the tank thermal models, needed for when the aircraft is stationary on the ground.
• Moves the calculation of the tank fuel densities to wsize() from read_input().
• Eliminates old functions in the src/fuel folder that have now been replaced.
• Introduces tests for the new CryoTank module.
• Adds DifferentialEquation.jl package for ODE solving. The ODE solver in the PEMFC models has been replaced by this.
• Documents the new tank model.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 55.76923% with 161 lines in your changes are missing coverage. Please review.

Project coverage is 74.44%. Comparing base (c224dd9) to head (ad57395). Report is 36 commits behind head on main.

Files	Patch %	Lines
src/cryo_tank/tanktools.jl	0.00%	131 Missing :warning:
src/sizing/wsize.jl	0.00%	14 Missing :warning:
src/cryo_tank/pressure.jl	79.66%	12 Missing :warning:
src/IO/read_input.jl	0.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #40 +/- ## ========================================== - Coverage 74.73% 74.44% -0.30% ========================================== Files 69 71 +2 Lines 13089 13381 +292 ========================================== + Hits 9782 9961 +179 - Misses 3307 3420 +113 ```

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[ngomezve]

My next PR will introduce a regression test for a hydrogen aircraft sizing that will improve test coverage.

[ngomezve]

Updated to remove merge conflicts with PR 42

[ngomezve]

The ODE solver in DifferentialEquations.jl is now used instead of the custom RK4 one.