Replace Commons IO and Codec usages

[Goooler]

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• CHANGELOG's "Unreleased" section has been updated, if applicable.

[Copilot]

Pull request overview

This PR removes runtime dependencies on Apache Commons Codec and Commons IO by replacing their usages with equivalent JDK implementations, and updates tests and dependency declarations accordingly.

Changes:

• Replaced SHA-256 hashing implementation with MessageDigest + HexFormat and added a unit test for sha256Hex().
• Replaced CloseShieldOutputStream usage from Commons IO with a small local implementation to prevent closing the underlying JAR output stream.
• Removed Commons Codec/IO from Gradle dependency declarations and documented the change in the changelog.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/transformers/DeduplicatingResourceTransformer.kt	Replaces Commons Codec hashing with a JDK-based SHA-256 hex implementation.
src/test/kotlin/com/github/jengelman/gradle/plugins/shadow/transformers/DeduplicatingResourceTransformerTest.kt	Adds coverage for the new sha256Hex() behavior.
src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/transformers/Log4j2PluginsCacheFileTransformer.kt	Replaces Commons IO CloseShieldOutputStream with a local close-shielding wrapper.
src/main/kotlin/com/github/jengelman/gradle/plugins/shadow/relocation/SimpleRelocator.kt	Replaces Commons IO path parsing with simple string-based splitting.
build.gradle.kts	Removes Commons Codec/IO dependencies from the build.
gradle/libs.versions.toml	Removes version catalog entries for Commons Codec/IO.
docs/changes/README.md	Adds a changelog entry describing the dependency removal.

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