chore: fix Swift 6 warnings and deprecated API usage

[hyochan]

Summary

Fix compiler warnings identified during CI builds to prepare for Swift 6 compatibility and address deprecated API usage.

Warnings to Address

Swift 6 Compatibility (Priority: High)

File	Line	Warning	Fix
RnIapHelper.swift	8	class 'OpenIapException' must restate inherited '@unchecked Sendable' conformance	Add explicit @unchecked Sendable conformance
HybridRnIap.swift	136	reference to captured var 'products' in concurrently-executing code	Capture products as a local constant before closure

Unused Results (Priority: Low)

File	Line	Warning	Fix
HybridRnIap.swift	332	result of call to 'run(resultType:body:)' is unused	Add _ = or use @discardableResult

Deprecated API Usage (Priority: Medium)

File	Line	Warning	Fix
HybridRnIap.swift	355	'validateReceiptIOS' is deprecated: Use verifyPurchase	Migrate to verifyPurchase when removing deprecated API
HybridRnIap.swift	540	'requestPurchaseOnPromotedProductIOS()' is deprecated	Migrate to promotedProductListenerIOS + requestPurchase

Notes

• Swift 6 compatibility warnings should be prioritized as they will become errors in Swift 6
• Deprecated API warnings are from OpenIAP library - coordinate with OpenIAP updates
• react-native-nitro-modules warnings (AnyMapHolder.hpp deprecated) will be resolved when updating the Nitro Modules dependency

Related

Found during CI build of #3145