Improve warnings in AD rules

[lkdvos]

Adds some extra infomation to the AD gauge-dependence warnings:

• which function it is a contangent for
• severity of dependence

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 81.44%. Comparing base (370dd92) to head (0a3c649).
Report is 2 commits behind head on master.

Files	Patch %	Lines
ext/TensorKitChainRulesCoreExt.jl	50.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #122      +/-   ##
==========================================
- Coverage   81.46%   81.44%   -0.02%     
==========================================
  Files          42       42              
  Lines        5588     5588              
==========================================
- Hits         4552     4551       -1     
- Misses       1036     1037       +1     

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[Jutho]

Maybe remove the warnings above, have a single warning below the end and replace the aUΔUpart_norm and aVΔVpart_norm parts, i.e. as follows:

gaugepart = norm(view(aUΔU, mask) + view(aVΔV, mask), Inf)
if p > r
  rprange = (r + 1):p
  gaugepart = max(gaugepart, norm(view(aUΔU, rprange, rprange), Inf))
  gaugepart = max(gaugepart, norm(view(aVΔV, rprange, rprange), Inf))
end
gaugepart < tol ||
         @warn "`svd` cotangents sensitive to gauge choice: (|ΔGauge| = $gaugepart)"