The key purpose is handling all mscclpp objects' memory internally by
hiding shared pointers from user APIs.
* `Connection` class is now a wrapper of `BaseConnection` class that is
equivalent to the previous `Connection` class
* `connect()` methods now return `Connection` instead of
`std::shared_ptr<Connection>`
* Removed `connectOnSetup()` method
* Allow CudaIpc connection between GPUs in a single process
* Added an example of connection in a single process
* Minor interface updates
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Co-authored-by: Binyang Li <binyli@microsoft.com>
