fix(core): docs.rs on Windows and macOS

[lucasfernog]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

[chippers]

I don't mind the __isolation-docs workaround if ring itself if causing cargo doc to fail. We just will want to make sure that is what causes it. The suggested change makes it a single compile-time error if it is somehow used without enabling the isolation feature or the isolation docs workaround, along with making using it with only the docs workaround a runtime error since it's not secure.

[lucasfernog]

I tested the doc generation directly using the docs.rs repo and ring was one of the issues, so i had to disable it.