Add runnable count(local) examples to the Count Step docs

[spmallette]

The count(local) behavior in the Count Step section of the reference documentation was described only in an IMPORTANT prose callout, with no executable examples. The callout also omitted the Path case: it stated that a count of 1 is returned "for any other object," but CountLocalStep returns the path length for a Path.

This change:

• Removes the prose-only callout and repurposes its content as explanatory prose that correctly covers all object kinds the step handles: Collection (number of elements), Map (number of entries), Path (number of objects in the path), and any other object (1).
• Adds a runnable example block against the modern graph so the per-object-kind counts render as live output at build time and are self-verifying:
  • g.V().fold().count(local) → 6 (Collection)
  • g.V().group().by(label).count(local) → 2 (Map)
  • g.V(1).out().path().count(local) → 2, 2, 2 (Path)
  • g.V(1).count(local) → 1 (any other object)
• Cross-links the examples to fold(), group(), path(), and the path data structure so a reader can follow the behavior in context.

The reference book builds and the count-step section reads coherently with the rendered live output matching the documented counts.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.51%. Comparing base (4722890) to head (cabf641).
⚠️ Report is 44 commits behind head on 3.7-dev.

Additional details and impacted files

@@              Coverage Diff              @@
##             3.7-dev    #3573      +/-   ##
=============================================
+ Coverage      75.49%   75.51%   +0.01%     
- Complexity     13161    13178      +17     
=============================================
  Files           1092     1093       +1     
  Lines          67208    67254      +46     
  Branches        7391     7397       +6     
=============================================
+ Hits           50742    50789      +47     
- Misses         13837    13840       +3     
+ Partials        2629     2625       -4     

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[spmallette]

Merged with 06e12a8