Factor shrink loggers

[jmid]

This PR pulls out the shrink logging from the expect tests as it was cluttering the .expected output files needlessly and conflating

• checking basic functionality and
• highlighting the underlying shrinking algorithms (and their potential limitations).

There is now a separate directory shrink_algo_logs with a bunch of expect tests.
The idea is that these (in some cases terrifying) expect logs should gradually become nicer as each limitation is addressed 😀
One could say it turns a bunch of prior shrinking algorithm observations scattered around in comments into actual tests for everyone to see and improve on.

Highlights (many of which have been observed before):

• char_char_never_abcdef* logs how QCheck.char doesn't shrink (issue QCheck.char doesn't shrink (but QCheck2.Gen.char does) #166)
• fun_{first,last}_foldleftright_qcheck{,2}.expected shows how the QCheck function shrinker's "generate-function-last-for-best-result" comes at a price of many shrink steps (room for algorithmic improvement?) and that QCheck2's function shrinker also could use a helping hand (issue Sub-optimal QCheck2 function shrinkers #163)
• the int_* tests show QCheck2 repeatedly tests for 0 (aggressive shrinking - see below)
• list_shorter* shows how QCheck2 will try new random lists rather than cut down the first counterexample
  and 2 limitations of QCheck design (issue List shrinker performance #64):
  • (1) it wastes many needless shrink steps to restart and try smaller sizes repeatedly
  • (2) an aggressive int shrinker (trying 0 first like QCheck2) could cut down a number of steps (and restarts!)
• string_empty* shows how QCheck doesn't shrink the string's characters (mentioned in issue Improve QCheck2 string shrinking #157)
• string_never_has_000* shows how QCheck2's string shrinker tries random (unrelated) strings to cut down the size, while QCheck's shrink algorithm uses a simple iterative algorithm rather than bisection or something list-shrinking-inspired (both mentioned in Improve QCheck2 string shrinking #157).

Finally, it

• renamed test.ml to a more descriptive name
• simplified the dune logic
• removed shrink logging from existing tests and expect-outputs

[jmid]

(also paging @sir4ur0n which I couldn't add as a reviewer)

[sir4ur0n]

I am in vacation but if you're in no hurry I can review when I'm back 😄

[Gbury]

The split is nice ! The diff is quite long so I didn't read everything, but considering it's only some more tests, it can't be wrong, ^^

[Gbury]

it's a bit of a problem that this doesn't not shrink, or am I missing something ?

[jmid]

I characterized it as "debatable" myself when I added the tests originally 😉
#153 (comment)
incl. what I saw as arguments for and against.

There's also a level-headed reply from @sir4ur0n here:
#153 (comment)