Making IdealGasThermo compatible with Forward Differentiation

[ngomezve]

This PR introduces parametric typing for the Gas1D and Gas objects. In the current version, parameters inside these objects are typed as Float64,and so are the inputs to most functions. By relaxing the typing, the package can be compatible with Dual types, which are used by forward-mode automatic differentiation packages such as ForwardDiff.jl.

The PR introduces a new way to instantiate Gas objects via Gas(T,P), with the appropriate typing for the gas parameters being inferred from the inputs.

Tests on automatic differentiation are also included, comparing against finite differences.

[ngomezve]

This addresses issue #10

[codecov]

Codecov Report

❌ Patch coverage is 85.40541% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.52%. Comparing base (a0fe14a) to head (6db1603).

Files with missing lines	Patch %	Lines
src/Gas.jl	84.70%	13 Missing ⚠️
src/Gas1D.jl	54.54%	10 Missing ⚠️
src/combustion.jl	89.47%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #10      +/-   ##
==========================================
- Coverage   81.54%   81.52%   -0.02%     
==========================================
  Files          11       13       +2     
  Lines         791      812      +21     
==========================================
+ Hits          645      662      +17     
- Misses        146      150       +4     

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