🔒 Remove unsafe force unwrapping of optionals

[jhurt]

🎯 What:
Removed all implicitly unwrapped optionals (!) and force unwraps throughout GBPageControl/PageControl.swift.

⚠️ Risk:
Unsafe force unwrapping of optionals exposes the library to crash vulnerabilities (Denial of Service). If arrays are empty, integer counts are 0, or nodes are unexpectedly nil during standard execution or via gesture tampering, a force unwrap causes an immediate, unrecoverable crash of the host application.

🛡️ Solution:

• Converted implicitly unwrapped optional variables to standard optionals (?) or assigned safe default initial values (e.g., SKNode(), [], 0).
• Implemented guard let and if let statements across critical path methods like handleTouch, getSelectedPage, and handlePanGesture to safely bind and access optionals.
• Updated loops from 0...count - 1 to 0..<count to resolve out-of-bounds array crashes.

(Note: Unable to natively verify with a test suite as the current environment lacks swift and xcodebuild CLI tools, but visually verified syntactical safety.)

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PR created automatically by Jules for task 5951392591658611571 started by @jhurt

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