Stream blob uploads when digest/size are already known (no temp files)

[h2cone]

What would you like to be added?

Current OCI.pushBlob(ref, InputStream) spools to a temp file first (src/main/java/land/oras/OCI.java:109).

Add a streaming upload overload for the remote registry path, scoped to the "digest already known" case:

• New API (Registry):
  Layer pushBlob(ContainerRef refWithDigest, long size, Supplier<InputStream> stream, Map<String,String> annotations)

Constraints / behavior:

• refWithDigest.getDigest() is required; otherwise throw.
• Implement upload as distribution-spec two-step: POST /blobs/uploads/ (no body) -> PUT <location>?digest=... (single streamed body).
• Use BodyPublishers.ofInputStream(stream) so auth/redirect retries can reopen the stream (no temp files).

Copy usage:

• Update src/main/java/land/oras/CopyUtils.java to call the new overload and pass known layer.getSize() + a stream supplier.

Non-goals:

• Streaming when digest is not known (no "compute digest while uploading" in this change).
• Changing existing pushBlob(Path|byte[]) behavior.

Why is this needed for ORAS?

• Performance: avoid extra disk I/O and temp space for every copied blob.
• Resource limits: works in constrained environments (CI runners, k8s, serverless).

Are you willing to submit PRs to contribute to this feature?

• Yes, I am willing to implement it.