[core] Use shared_ptr for pins_in_flight_ instead of shared_from_this

[edoakes]

While writing the follow up to ban stack-allocated RayletClient instances, @dayshah proposed a simpler solution: make the counter a shared_ptr instead of capturing the entire class.

[gemini-code-assist]

Code Review

This pull request correctly refactors RayletClient to remove the dependency on std::enable_shared_from_this. By converting pins_in_flight_ to a std::shared_ptr<std::atomic<int64_t>>, you've effectively decoupled the lifetime of the counter from the RayletClient instance, allowing it to be safely used in asynchronous callbacks without requiring the client object to be managed by a shared_ptr. The implementation is clean and achieves the intended goal. I have one minor suggestion to improve the clarity of a lambda capture.

[edoakes]

@dayshah any clever C++ magic you have up your sleeve that could be used to ban people from unknowingly capturing this in a callback in the future?

[dayshah]

@dayshah any clever C++ magic you have up your sleeve that could be used to ban people from unknowingly capturing this in a callback in the future?

eh, you could have a wrapper class to create the callbacks, and the constructor could not take pointers and references. But imo not worth it...