Migrate Unzip task to use TaskEnvironment API

[Copilot]

Context

Migrates the Unzip task to use the TaskEnvironment API for thread-safe path resolution, following the pattern established in #12914. This enables the task to run safely in MSBuild's multithreaded execution model.

Changes Made

• Add IMultiThreadableTask interface and [MSBuildMultiThreadableTask] attribute to Unzip class
• Add TaskEnvironment property
• Replace Path.GetFullPath() with TaskEnvironment.GetAbsolutePath() for:
  • Destination folder creation
  • Source file path resolution
  • Extracted file path resolution (with zip-slip protection preserved)
• Update all unit tests to provide TaskEnvironmentHelper.CreateForTest() when instantiating the task

Testing

• All 14 Unzip unit tests pass
• Updated all test instantiations to provide TaskEnvironmentHelper.CreateForTest()

Notes

The zip-slip exploit protection check uses AbsolutePath.Value for string comparison to maintain the security validation while using thread-safe path resolution.

Original prompt

Migrate the Unzip task to use TaskEnvironment API based on the pattern used here: #12914

Make sure to preserve correctness, performance and that the tests pass

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[dotnet-policy-service]

Hello @@copilot, I noticed that you’re changing an .swr file or any file under src/Package/MSBuild.VSSetup.. Please make sure to validate this change by an experimental VS insertion. This is accomplished by pushing to an exp/* branch, which requires write permissions to this repo.

[JanProvaznik]

@copilot one comment

[Copilot]

Pull request overview

This PR migrates the Unzip task to use the TaskEnvironment API for thread-safe path resolution, enabling safe execution in MSBuild's multithreaded environment. This follows the established pattern from PR #12914 that migrated other file I/O tasks (Copy, Delete, MakeDir, RemoveDir, Touch).

Changes:

• Added IMultiThreadableTask interface and [MSBuildMultiThreadableTask] attribute to enable multithreaded execution
• Replaced process-global Path.GetFullPath() calls with thread-safe TaskEnvironment.GetAbsolutePath()
• Updated all 17 test cases to provide TaskEnvironment instances via TaskEnvironmentHelper.CreateForTest()

Reviewed changes

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

File	Description
src/Tasks/Unzip.cs	Added multithreadable task support and migrated three path resolution calls (destination folder, source file, extracted file path) to use TaskEnvironment API while preserving zip-slip security validation
src/Tasks.UnitTests/Unzip_Tests.cs	Updated all 17 Unzip task instantiations to include TaskEnvironment property initialization

[JanProvaznik]

blocked by #13120 for correctness