Fix cuda.core and cuda.bindings example links in docs

[uday1o1]

Summary

• Replace raw cuda.core and cuda.bindings GitHub example URLs that used |..._github_ref| substitutions with Sphinx extlinks roles.
• Update affected links in cuda_core/docs/source and cuda_bindings/docs/source.
• Preserve version-aware behavior so latest/preview docs link to main, while release docs link to the appropriate release tag/ref.

Root Cause

The GitHub ref replacements were defined through rst_epilog, but they were used inside embedded hyperlink URI targets. Sphinx/Docutils left those substitutions literal in generated HTML, so browsers/GitHub saw URLs containing values like |cuda_core_github_ref| or |cuda_bindings_github_ref|. Those are treated as branch/tag names and the links return 404.

Validation

• Crawled 250 live latest docs pages and found the affected pages were limited to cuda.core and cuda.bindings docs pages touched by this PR.
• Built Sphinx smoke docs for:
  • cuda.core latest
  • cuda.core release 1.0.1
  • cuda.bindings latest
  • cuda.bindings release 13.3.0
• Checked generated GitHub example links from all four smoke builds; all returned HTTP 200.
• Confirmed generated HTML no longer contains cuda_core_github_ref, cuda_bindings_github_ref, or encoded %7Ccuda_... refs.
• Ran git diff --check.

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