Don't force inlining--let Julia figure that out on its own

[ararslan]

We're currently forcibly inlining a lot of stuff. This is a draft PR to see what the ramifications would be of not doing any of that, and simply letting Julia figure out when it should inline. This is motivated by a comment from @willtebbutt: #145 (review).

[willtebbutt]

Looks good. I would be interested to know if there's anything that significantly slows down -- it would kind of surprise me if there were.

[ararslan]

It would surprise me as well. I'll put some benchmarks together, I just need to determine what would be the applications most affected by this change (if at all).

[codecov]

Codecov Report

Merging #160 into master will decrease coverage by <.01%.
The diff coverage is 87.87%.

@@            Coverage Diff             @@
##           master     #160      +/-   ##
==========================================
- Coverage   97.05%   97.05%   -0.01%     
==========================================
  Files          20       20              
  Lines         748      747       -1     
==========================================
- Hits          726      725       -1     
  Misses         22       22

Impacted Files	Coverage Δ
src/sensitivity.jl	100% <100%> (ø)	⬆️
src/sensitivities/scalar.jl	100% <100%> (ø)	⬆️
src/core.jl	93.61% <100%> (ø)	⬆️
src/sensitivities/functional/functional.jl	76.19% <60%> (-0.56%)	⬇️

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