Allow editing the testset name

[theogf]

Solves #272

Add a keyword argument "testset_name" to test_scalar, test_frule and test_rrule to allow replacing the default name.
It still stays an opt-in option and is mostly useful when f is anonymous and its naming is too large to be displayed correctly.

[codecov]

Codecov Report

Patch coverage: 57.14% and project coverage change: +0.14 🎉

Comparison is base (6925da1) 93.51% compared to head (ca519c6) 93.65%.

❗ Current head ca519c6 differs from pull request most recent head 2fd4943. Consider uploading reports for the commit 2fd4943 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
+ Coverage   93.51%   93.65%   +0.14%     
==========================================
  Files          12       12              
  Lines         339      347       +8     
==========================================
+ Hits          317      325       +8     
  Misses         22       22              

Impacted Files	Coverage Δ
src/testers.jl	91.50% <57.14%> (+0.24%)	⬆️
src/output_control.jl	100.00% <0.00%> (ø)
src/ChainRulesTestUtils.jl	100.00% <0.00%> (ø)

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[gaurav-arya]

Is this package meant to work on Julia 1.0? If so I think the isnothing check needs compat handling, see the broken tests on AbstractFFTs.jl

[gaurav-arya]

@devmotion is way ahead of me:)