⚡ Optimize IPtalkManager string concatenation

[SilentMalachite]

💡 What: Replaced the receivedText stored String property with a receivedTextSegments array of strings, exposing receivedText as a computed property that joins the segments.

🎯 Why: The previous implementation used += for string concatenation in processReceivedData, which can lead to $O(N^2)$ performance degradation as the text grows (due to repeated copying). Using an array of strings reduces the append complexity to amortized $O(1)$.

📊 Measured Improvement:

• Theoretical: $O(N^2)$ -> $O(N)$ (where N is total text length).
• Verification: A benchmark test (PerformanceTests.swift) was designed but could not be executed due to the Linux environment lacking macOS frameworks (Network, XCTest).
• Note: The logic ensures that newline handling remains identical to the original implementation. receivedText is now read-only, which matches its usage pattern (only written internally via processReceivedData and clearReceivedText).

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PR created automatically by Jules for task 28176032284257407 started by @SilentMalachite

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[Copilot]

Pull request overview

This PR optimizes how IPtalkManager accumulates received text to avoid quadratic-time string concatenation, while preserving the observable interface used by the UI.

Changes:

• Replaced the mutable receivedText: String stored property with a private receivedTextSegments: [String] plus a computed receivedText that joins the segments.
• Updated processReceivedData(_:) to append incoming text and optional newlines to receivedTextSegments instead of concatenating onto a single String.
• Updated clearReceivedText() to clear receivedTextSegments, keeping the external API (receivedText and clearReceivedText()) behaviorally consistent.

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[Copilot]

The new computed receivedText now joins the entire receivedTextSegments array on every access, which turns each read into an O(N) operation and can cause extra allocations, especially since SwiftUI accesses this property multiple times per render (for Text, isEmpty checks, and button state). To preserve the append-time optimization without introducing a potential read-time bottleneck, consider caching the joined string and invalidating/rebuilding it only when receivedTextSegments changes (e.g., track a dirty flag or similar).

Suggested change

	private var receivedTextSegments: [String] = []
	var receivedText: String {
	receivedTextSegments.joined()
	private var receivedTextSegments: [String] = [] {
	didSet {
	receivedTextCache = receivedTextSegments.joined()
	}
	}
	private var receivedTextCache: String = ""
	var receivedText: String {
	receivedTextCache

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