test(storage): add and improve tests for MultiRangeDownloader

[cpriti-os]

• The previously skipped TestIntegration_ReadSameFileConcurrentlyUsingMultiRangeDownloader test has been unskipped and refactored. It now uses sync.WaitGroup for managing concurrency, increases the test object size to 10MB, and randomizes offset/limit values for Add calls to better simulate varied request patterns and stress the internal event loop.
• New MultiRangeDownloader Retry Conformance Tests: Three new conformance tests have been added for the MultiRangeDownloader. These tests verify retry behavior for multiple concurrent requests on a single stream, ensure correct error handling for invalid download ranges (returning codes.OutOfRange), and confirm mid-stream resumption capabilities for large object downloads.

[gemini-code-assist]

Summary of Changes

Hello @cpriti-os, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the test coverage and robustness of the MultiRangeDownloader component. It addresses a previously flaky integration test by refactoring its concurrency model and introduces several new conformance tests to validate retry mechanisms, concurrent range handling, and error conditions, ensuring more reliable and predictable behavior of the downloader.

Highlights

• MultiRangeDownloader Concurrent Test Refactor: The previously skipped TestIntegration_ReadSameFileConcurrentlyUsingMultiRangeDownloader test has been unskipped and refactored. It now uses sync.WaitGroup for managing concurrency, increases the test object size to 10MB, and randomizes offset/limit values for Add calls to better simulate varied request patterns and stress the internal event loop.
• New MultiRangeDownloader Retry Conformance Tests: Three new conformance tests have been added for the MultiRangeDownloader. These tests verify retry behavior for multiple concurrent requests on a single stream, ensure correct error handling for invalid download ranges (returning codes.OutOfRange), and confirm mid-stream resumption capabilities for large object downloads (3MiB).
• Dependency Update: The golang.org/x/sync/errgroup dependency was removed from storage/integration_test.go as the concurrent test logic was refactored to use sync.WaitGroup instead.

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[gemini-code-assist]

Code Review

This pull request adds and improves tests for MultiRangeDownloader. The improvements to the concurrent read test in storage/integration_test.go are excellent, making the test more robust by using varied, non-overlapping range requests. New retry conformance tests have also been added. However, there is a critical issue in storage/retry_conformance_test.go where the new tests are placed under the wrong API method, which needs to be corrected.

[tritone]

Thanks for adding these, couple comments but generally looks good.