Use uint.TryFormat to fix TODO in IPAddressParser

[stephentoub]

No description provided.

[Copilot]

Pull Request Overview

This PR replaces the manual digit-by-digit formatting of the IPv6 scope ID with a call to uint.TryFormat, removing the TODO and reducing code complexity.

• Added a Debug.Assert to ensure TChar is either byte or char.
• Replaced manual stackalloc formatting with a single TryFormat call for both byte and char.
• Removed the old loop-based formatting and related TODO comment.

Comments suppressed due to low confidence (1)

src/libraries/System.Net.Primitives/src/System/Net/IPAddressParser.cs:225

• Add unit tests covering the new TryFormat logic for both TChar = char and TChar = byte to ensure the IPv6 scope ID formatting is exercised in all scenarios.

                bool formatted = typeof(TChar) == typeof(byte) ?

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