Implement caching and improve PNG generation performance

[sweep-ai[bot]]

This pull request was created by Sweep to resolve the following request by @harperreed:

6. [ ] Optimize image generation
   • [ ] Investigate using sharp for faster image processing
   • [ ] Implement pre-generation and caching of common identicons

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Purpose

This pull request aims to improve the performance and caching of the identicon generation functionality in the effigy.im project.

Description

The key changes in this pull request are:

1. Implemented a caching mechanism using the node-cache library to store generated identicons. This will reduce the need to generate new identicons on every request, improving overall response times.
2. Optimized the PNG identicon generation process by using the sharp library, which provides faster image processing compared to the previous pnglib implementation.
3. Refactored the blockiesPNG.js module to use the new sharp-based implementation, improving the overall code quality and maintainability.

Summary

The changes in this pull request include:

• Implemented a caching mechanism using node-cache in functions/index.js
• Optimized the PNG identicon generation process using the sharp library in functions/lib/blockiesPNG.js
• Refactored the blockiesPNG.js module to use the new sharp-based implementation