Remove commons-io dependency from Azure Cosmos Spark

[alzimmermsft]

Description

Replace single, basic API usage from commons-io to remove dependency on it, removing a CVE warning from our scanning system.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull request overview

This PR removes the commons-io dependency from the Azure Cosmos Spark connector to eliminate CVE warnings. The single usage of IOUtils.toString() has been replaced with a custom implementation that reads from a Reader and converts it to a String.

Key Changes

• Removed commons-io dependency from pom.xml (both dependency declaration and allowedExternalDependency list)
• Implemented custom readerToString method to replace IOUtils.toString(Reader)
• Added internal StringBuilderWriter class to support the custom implementation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
sdk/cosmos/azure-cosmos-spark_3/src/main/scala/com/azure/cosmos/spark/ChangeFeedInitialOffsetWriter.scala	Replaced IOUtils.toString with custom readerToString implementation and added StringBuilderWriter helper class
sdk/cosmos/azure-cosmos-spark_3/pom.xml	Removed commons-io dependency from both dependencies section and allowed external dependencies list