Make InferenceData and Dataset type-unstable

[sethaxen]

Fixes #15 by removing type annotations from InferenceData and Dataset. This makes high-order operations on these types compile quickly (and possibly automatically precompile), while operations on arrays are still compiled for the specific dimensions of that array and so are still fast.

[codecov-commenter]

Codecov Report

Merging #24 (676e82d) into main (766efd4) will increase coverage by 0.66%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #24      +/-   ##
==========================================
+ Coverage   97.08%   97.75%   +0.66%     
==========================================
  Files          10        9       -1     
  Lines         309      312       +3     
==========================================
+ Hits          300      305       +5     
+ Misses          9        7       -2     

Impacted Files	Coverage Δ
src/dataset.jl	92.30% <ø> (ø)
...ferenceObjectsNetCDF/src/InferenceObjectsNetCDF.jl	95.77% <100.00%> (+0.12%)	⬆️
src/from_namedtuple.jl	97.29% <100.00%> (ø)
src/inference_data.jl	100.00% <100.00%> (+3.03%)	⬆️
src/utils.jl	100.00% <0.00%> (ø)
src/InferenceObjects.jl

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[sethaxen]

I'd like to in this PR also explore the feasibility of making Dataset have dictionary storage instead of NamedTuple. I expect this will eliminate even more compile time lag, e.g. show, and will allow new variables to be added to existing datasets.

[sethaxen]

Supporting mutable and type-unstable Dataset will require some changes to DimensionalData (see rafaqz/DimensionalData.jl#457), so that will wait for another PR in a future breaking release.