Shorten printing of Tangent and thunks

[mcabbott]

[codecov-commenter]

Codecov Report

Merging #564 (97b28df) into main (2f76da0) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 97b28df differs from pull request most recent head f5e9387. Consider uploading reports for the commit f5e9387 to get more accurate results

@@            Coverage Diff             @@
##             main     #564      +/-   ##
==========================================
+ Coverage   93.02%   93.03%   +0.01%     
==========================================
  Files          15       14       -1     
  Lines         860      862       +2     
==========================================
+ Hits          800      802       +2     
  Misses         60       60              

Impacted Files	Coverage Δ
src/tangent_types/tangent.jl	85.71% <100.00%> (+0.42%)	⬆️
src/tangent_types/thunks.jl	95.65% <100.00%> (+0.28%)	⬆️
src/accumulation.jl	97.14% <0.00%> (-0.08%)	⬇️
src/rule_definition_tools.jl	96.79% <0.00%> (-0.07%)	⬇️
src/projection.jl	97.26% <0.00%> (-0.05%)	⬇️
src/ChainRulesCore.jl

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[oxinabox]

I am ok with this.
If the user really needs that info, it is still printed in show(typeof(tangent))

Maybe add a comment being explaining what it is doing?
Like else # replace over long part with ... ?

Also can we add a test?
It doesn't have to check the actual text produced but make it check that the result of something that would have a very long print is indeed short.

Once that is done merge when happy