Fix vertex_ids_t -> edge_id_t in docs

[mlyoung101]

Some docs pages refer to vertex_ids_t, which has since been replaced by edge_id_t.

[github-actions]

Hi there! Thank you for creating your first pull-request on the Graaf library :)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.58%. Comparing base (e0ec371) to head (895f4c5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #300      +/-   ##
==========================================
- Coverage   99.60%   99.58%   -0.03%     
==========================================
  Files          59       59              
  Lines        2776     2621     -155     
  Branches      136      136              
==========================================
- Hits         2765     2610     -155     
  Misses         11       11              

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[bobluppes]

Nice, LGTM