refactor(functions/v2/imagemagick): migrate from gm to sharp

[angelcaamal]

Description

Fixes Internal: b/503435756

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Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

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[gemini-code-assist]

Code Review

This pull request replaces the gm library with sharp for image processing. The changes include updating the blurring logic to use sharp's asynchronous API, introducing a separate temporary path for blurred images, and ensuring all temporary files are cleaned up in a finally block. Additionally, tests were updated to remove the requirement for system-level ImageMagick installation. A potential issue was identified regarding the sharp version compatibility with the Node.js version specified in the engines field of package.json.

[iennae]

@angelcaamal can you resolve the linting issue I added with the check for the buckets? Thank you!

Overall, this looks like a solid update. I'm wondering whether we can do a streaming version that would simplify the code but we shouldnt' change it here. more details internally, but once you resolve linting I think this is good.