ref: Renames `SentrySpan` class to `SentrySpanInternal`

[github-actions]

Note

The pull request "ref: Renames SentrySpan class to SentrySpanInternal" was created by @itaybre but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

📜 Description

Renames the class SentrySpan to SentrySpanInternal, keeping SentrySpan only to the protocol.
Only the protocol is a public API, so no breaking changes were made

💡 Motivation and Context

We have 2 types with identical names, one a protocol and another a class.
While converting the SentryCrashIntegration to Swift, I ran into issues with them having the same name in ObjC.

💚 How did you test it?

📝 Checklist

You have to check all boxes before merging:

• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

[linear]

COCOA-1145