Update cats ecosystem to CE3

[pomadchin]

This PR is based on #609 and #608 and supersedes these PRs.

cc @custommonkey and @Daenyth

Closes #609
Closes #608
Closes #607

[codecov]

Codecov Report

Merging #616 (9fac9f7) into master (18fc6d2) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #616   +/-   ##
=======================================
  Coverage   95.15%   95.15%           
=======================================
  Files          65       65           
  Lines        1157     1157           
  Branches        7        7           
=======================================
  Hits         1101     1101           
  Misses         56       56           

Flag	Coverage Δ
2.12.15	95.15% <100.00%> (ø)
2.13.8	95.78% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cats/src/main/scala/frameless/cats/implicits.scala	73.91% <ø> (ø)
...rc/main/scala/frameless/cats/FramelessSyntax.scala	100.00% <100.00%> (ø)

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[custommonkey]

Works for me 👍🏼

[pomadchin]

Merging this in, thx @custommonkey and @Daenyth for the initial step, investigations, and doc updates 🚀