feat: cache SHA3-384 entries

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The Binstore only publishes SHA3-384 hashes for bins. This PR enables storing entries in the cache using
SHA3-384 hashes. Consumers of the cache package must now explicitly select the algorithm to
be used to create/write/read an entry.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR extends the internal cache to support multiple hashing algorithms (SHA-256 and SHA3-384) and updates callers/tests to specify which algorithm to use.

Changes:

• Introduced hashAlgo with SHA-256 and SHA3-384 support, plus hash construction via newHash.
• Updated cache APIs (Create, Write, Open, Read) to take an algorithm parameter and adjusted archive fetch code accordingly.
• Added a test verifying SHA3-384 entries are isolated from SHA-256 entries.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
internal/cache/cache.go	Adds multi-algorithm hashing support, updates cache APIs, and expires entries across algorithm directories.
internal/cache/cache_test.go	Updates tests to pass the algorithm and adds SHA3-384 isolation coverage.
internal/archive/archive.go	Updates cache usage in archive fetch path to specify SHA-256 algorithm.

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