Experiment info fragility

[scheibelp]

Fixes #1168
... kind of

Also fixes the case where if you specify a wrong variant value, that benchpark was saying the variant doesn't exist

Right now, to print out all the experiment info we want, we have to actually instantiate it, which means we need to provide a valid spec, so just a name isn't always possible. This "fixes" the problem described in 1168 by reporting more info. There's quite a bit of exception output though, so annoying for a user to sift through.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 57.89474% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.42%. Comparing base (41fa7f6) to head (5b240a9).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
lib/benchpark/cmd/info.py	22.22%	7 Missing ⚠️
lib/benchpark/spec.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1247      +/-   ##
===========================================
+ Coverage    62.83%   64.42%   +1.59%     
===========================================
  Files           48       48              
  Lines         3643     3657      +14     
  Branches       279      283       +4     
===========================================
+ Hits          2289     2356      +67     
+ Misses        1345     1292      -53     
  Partials         9        9              

Files with missing lines	Coverage Δ
lib/benchpark/spec.py	86.64% <90.00%> (+0.01%)	⬆️
lib/benchpark/cmd/info.py	23.80% <22.22%> (-0.36%)	⬇️

... and 2 files with indirect coverage changes

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