fix: PointcareDisk.sty missing canvas def

[cmumatt]

Description

In the hyperbolic domain example set, PointcareDisk.sty lacks a canvas definition. This PR resolves that issue.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new ESLint warnings

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[codecov]

Codecov Report

Merging #851 (4e53638) into main (20409e4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #851   +/-   ##
=======================================
  Coverage   68.25%   68.25%           
=======================================
  Files          62       62           
  Lines        8058     8058           
  Branches     1812     1812           
=======================================
  Hits         5500     5500           
  Misses       2478     2478           
  Partials       80       80           

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