feat: demonstrate per-hook evaluation exposure deduplication

[abelonogov-ld]

Summary

• Adds a Swift demo (ExposureCountingHook + ExposureDedupeDemo) that registers two hooks with 5s and 10s evaluationExposureDeduper windows — the same per-hook, opt-in API as ios-client-sdk#516.
• Updates the iOS UI with Evaluate / Identify controls and live before/after counts so repeated evaluations and identify resets are easy to verify.
• Points the Podfile at the andrey/flag-exposure-dedupe SDK branch until that work is released; watchOS still uses LDClientConfigurator without hooks.

Test plan

• pod install and open hello-ios.xcworkspace
• Set ExposureDedupeDemo.mobileKey and a boolean featureFlagKey
• Run the iOS target; tap Evaluate Flag repeatedly — requested count climbs while each hook's count stays flat until its window elapses
• Tap Identify with an empty key — both hook caches clear and the next evaluate increments both again
• Confirm watchOS still builds / starts via LDClientConfigurator

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[tanderson-ld]

The hello apps are meant to demonstrate default configuration applications initializing and do basic flag evaluation. Since we have not agreed that deduping should be a default mobile behavior, I don't think this is mergable. The hello apps are not meant to be a demonstration of various configuration options / feature demos. That would be something for the docs pages.

SDK Spec HELLO-hello-apps has The Hello App SHOULD initialize using the default config.