feat: put public completions into main-thread (makes it Swift6 compatible)

[abelonogov-ld]

Requirements

Put completions of all public methods into main-thread.

1. Solves inconsistency of completion on unexpected threads. (before some was on main and some not)
2. Solves Obj-C compatibility
3. Solves using library from Swift6 project

Related issues

(#419)

Describe the solution you've provided

Provide a clear and concise description of what you expect to happen.

Describe alternatives you've considered

Require customers wrap completions into sendable completions. T

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Note

Standardizes completion threading across the public API to always invoke on the main thread.

• setOnline(_:completion:): wraps DispatchGroup.notify to hop to DispatchQueue.main before calling completion
• identify(...): introduces _identifyMain that dispatches result to main; all identify overloads now route through it (including deprecated variant)
• start(config:context:completion:) and start(config:context:startWaitSeconds:completion:): wrap provided completions to execute on main
• Minor refactor: replace direct _identifyHooked calls with _identifyMain in public paths; internal behavior unchanged

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[tanderson-ld]

If an existing customer is doing an operation that requires a non-ui thread in the completion, could this be considered a breaking change?

For example: an existing customer does a network operation or database operation in the completion. If they adopt this update in a minor version, it would introduce a bug for them.

Is it possible that for v10 we add an optional param for the callback dispatch queue?