fix(ios): make WebView configuration callback non-optional for Swift

[Yaswanth0606]

Summary

• The JuspayWebViewConfigurationCallback block typedef introduced in 5.0.36 carries no nullability, so Swift imports it as (WKWebView?) -> Void and merchants have to unwrap the web view before handing it to Minkasu — unlike the Flutter plugin ((WKWebView) -> ()) and the SDK's own onWebViewReady:(WKWebView * _Nonnull).
• Mark the block parameter _Nonnull, so Swift now sees (WKWebView) -> Void.
• Mark the setter argument nullable, so passing nil to clear the callback is explicit (the implementation already handles it).
• Landing this before merchants adopt 5.0.36 avoids a source-breaking change later: a guard let webView = webView written against the optional signature stops compiling once the type becomes non-optional.

No other declarations in HyperSdkReact.h are touched, so this adds no nullability warnings beyond what 5.0.36 already emits.

Test plan

• swiftc -typecheck of a merchant snippet with the closure explicitly typed (webView: WKWebView): compiles with this change; fails against 5.0.36 with cannot convert '(WKWebView) -> ()' to '(Optional<WKWebView>) -> ()'. setJuspayWebViewConfigurationCallback(nil) is accepted.
• clang syntax check of the new declarations under -Werror.
• pod install in the example app and confirm the Minkasu callback receives the WKWebView on a real bank page.

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