get_raw_blob: Properly handle -1 return from GetRawBlob

[cgwalters]

Just like GetBlob, the size might not be known. In the case of this API, one use case is being driven from e.g. https://github.com/cgwalters/cstor-dist
which is exposing a HTTP API, so it's really useful for us to have the size here so that server can in turn provide it via its own Content-Length if available.

[gemini-code-assist]

Summary of Changes

Hello @cgwalters, 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 enhances the get_raw_blob API to gracefully handle scenarios where the size of the fetched blob is not immediately known. By introducing an optional return type for the blob length, the system can now communicate the absence of size information, improving the API's robustness and utility for external services that rely on this data.

Highlights

• get_raw_blob function signature change: The get_raw_blob function now returns Option for the blob size instead of u64, allowing it to properly handle cases where the size is unknown (represented by -1 from the underlying GetRawBlob call).
• Robust size handling: The change ensures that the GetRawBlob API can correctly propagate an unknown blob size, which is crucial for consumers like HTTP servers that might need to provide a Content-Length header.

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[cgwalters]

This is a semver break, but we already bumped semver in #91

[gemini-code-assist]

Code Review

This pull request correctly adapts the get_raw_blob function to handle cases where the blob size is unknown, indicated by a -1 value from the proxy. The function signature is updated to return an Option<u64> for the size, which is a breaking but necessary change. The implementation correctly deserializes the potentially negative size as an i64 and then converts it to an Option<u64>. The changes are sound and well-implemented.

[cgwalters]

Followup to #97