feat(docs): parallel PR spec-doc builds, publish-only social cards

[spencer-tb]

🗒️ Description

Aims to improve per PR docs CI workflows.

Spec doc builds now run as four parallel docc shards over consecutive fork sets cutting Build Spec Docs to ~4m.

MkDocs social cards are now publish only, trimming Build HTML Docs to ~5mins.

🔗 Related Issues or PRs

N/A.

✅ Checklist

• All: Ran fast static checks to avoid unnecessary CI fails, see also Code Standards and Verifying Changes:

  just static

• All: PR title have the form <type>(<area>):, where <type> and <area> come from an approrpriate C-<type>, respectively A-<area>, label. The title should match the a target squash commit message.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).

Cute Animal Picture

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.30%. Comparing base (64ed676) to head (653c646).
⚠️ Report is 10 commits behind head on forks/amsterdam.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           forks/amsterdam    #3101      +/-   ##
===================================================
+ Coverage            93.23%   93.30%   +0.07%     
===================================================
  Files                  624      624              
  Lines                36924    36986      +62     
  Branches              3373     3383      +10     
===================================================
+ Hits                 34427    34511      +84     
+ Misses                1704     1693      -11     
+ Partials               793      782      -11     

Flag	Coverage Δ
unittests	93.30% <ø> (+0.07%)	⬆️

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