Re-enable linkcheck for links to examples

The current approach to link to examples within the documentation breaks the linkcheck (and the documentation build) as the linked file is not available at runtime, even though it is available at build time.

See [this conversation](https://github.com/ansys-internal/pystk/pull/654#discussion_r2001706173) for an example.

Once a new approach is employed, the directive to ignore links to examples in the linkcheck should be removed.

No files or tests are named; start by reviewing linked pull request #1098 and the example conversation in pull request #654. Locate the directive that ignores links to examples and the documentation linkcheck configuration. Done means a new example-linking approach works at runtime and build time, and the ignore directive is removed.

Written by the indexing model from the issue text.