Move compatibility for non github.com targets to `github.With<THING>` options

I propose that all compatibility functionality not required for the github.com target be removed from the default client setup and only be included via a github.With<THING> option. This (hopefully) would make the default client surface area simpler to understand. The justification for this is that you already need to use github.WithEnterpriseURLs to target non github.com. I propose the following changes to adopt this pattern, with the potential for other capabilities (such as enabling/disabling preview endpoints) to be added later.

• Default to the latest API version (2026-03-10)
  • Functions that require a specific version now check against the client version and error if not valid
• Add github.WithAPIVersion to explicitly set a version
  • Set at the client/service level
• Add github.WithAdvancedServer to enable GHAS support
  • Better validation of inputs
  • Support setting version
  • Add compatibility accordingly
• Add github.WithEnterpriseCloud to enable GHEC support
  • Better validation of inputs
• Deprecate github.WithEnterpriseURLs

I'd appreciate any feedback on this proposal.

cc: @gmlewis - @alexandear - @zyfy29 - @Not-Dhananjay-Mishra - @munlicode