Minor release changes

• Update TracingMiddleware to follow updated OTel conventions. #736 from @slashmo
• Add upcoming feature ExistentialAny. #740
• Add upcoming feature MemberImportVisibility. #741
• Add upcoming feature InternalImportsByDefault. #741

## Patch release changes

• Make HTTP2 state machine non-copyable to avoid array copies. #717
• Update to use Swift Testing. #718

Other changes

• Fix typo in docc comment. #744 from @ole
• Update docc comments about Middleware application. #745
• Improve contribution guidelines. #734
• Fix code sample in README. #738 from @kattouf