Add CloseShieldChannel to close-shielded NIO Channels

[ppkarwasz]

Adds Channels.closeShield(Channel) to return a JDK proxy that preserves the delegate’s Channel sub-interfaces and shields the underlying channel from close().

Behavior

• close() flips shield state; delegate is not closed.
• isOpen() reflects shield state and delegates if shield is not closed.
• After shield-close, I/O/mutating methods throw ClosedChannelException; safe queries (e.g., NetworkChannel.supportedOptions()) still work.
• Fluent methods that return this (e.g., SeekableByteChannel.position/truncate, NetworkChannel.bind/setOption) return the proxy.
• Stable equals/hashCode/toString
• The method is idempotent (no double-wrapping).

Tests

• All methods of SeekableByteChannel / NetworkChannel and super-interfaces are tested.

[Copilot]

Pull Request Overview

This PR adds a new utility method Channels.closeShield(Channel) that creates a close-shield proxy for NIO channels. The proxy preserves the delegate's Channel sub-interfaces and shields the underlying channel from being closed when close() is called on the proxy.

• Introduces close-shielding functionality via JDK dynamic proxies
• Implements comprehensive handling of all Channel interface types
• Provides proper fluent method support and post-close behavior enforcement

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/main/java/org/apache/commons/io/channels/Channels.java	Main utility class with closeShield method and interface collection logic
src/main/java/org/apache/commons/io/channels/CloseShieldChannelHandler.java	InvocationHandler implementation for proxy behavior and method delegation
src/test/java/org/apache/commons/io/channels/ChannelsTest.java	Comprehensive test suite covering all Channel interfaces and edge cases
src/changes/changes.xml	Documentation update for the new feature

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[garydgregory]

@ppkarwasz TY. PR merged!