fix: etag issues identified in #11

[murfffi]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @murfffi, 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 focuses on resolving ETag-related issues within the download functionality by refining the logic for temporary file creation and enhancing error handling mechanisms. It significantly improves the testability of the download process through dependency injection for the HTTP client and introduces new dedicated tests for critical scenarios, leading to a more robust and reliable file fetching system.

Highlights

• Improved ETag Handling Logic: The logic for determining when to create temporary files during downloads has been refined, specifically addressing scenarios related to ETag usage.
• Enhanced Error Handling: Error wrapping using merry.Wrap has been introduced for file creation and closing operations, and a critical check for a nil response body was added to prevent potential panics during data copying.
• Testability Improvements: The fetchZip function was refactored to delegate to a new fetchZipWithClient function, which accepts an httpClient interface. This makes the HTTP client injectable, significantly improving the testability of the download logic.
• New Internal Tests: A new internal test file (download_internal_test.go) was added, including tests for fetchZipWithClient to cover edge cases such as empty response bodies and ETag handling.
• Dependency Update: The github.com/murfffi/gorich dependency has been updated from v0.2.0 to v0.2.1.

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[gemini-code-assist]

Code Review

This pull request addresses issues with ETag handling by correcting the logic for when to use ETag-based caching. To improve testability, fetchZip has been refactored to use an httpClient interface, and new unit tests have been added to cover edge cases like empty response bodies and missing ETags. The changes are solid, and my feedback focuses on making the error handling more idiomatic with the merry library.