OCI indexer

[luke-lombardi]

Note

Introduce OCI image indexing and runtime with checkpointed lazy reads, layered caching, and pluggable registry auth, plus extensive tests and build updates.

• OCI v2 Support:
  • Implement metadata-only OCI indexing (CreateFromOCIImage, IndexOCIImage) with layer whiteout handling, inode generation, and gzip checkpointing; writes OCIStorageInfo and RemoteRef entries.
  • Extend archive read/write to encode/decode OCI storage info; add gob registrations.
  • Add image metadata embedding (ImageMetadata, LayerMetadata).
• Storage:
  • New OCIClipStorage with 3-tier lazy reads: disk cache → content cache (range reads) → registry; optional checkpoint-based partial decompression.
  • Route in NewClipStorage to OCI backend; support cache/config options.
• Auth:
  • Pluggable RegistryCredentialProvider (env, Docker config, keychain, static, ECR, AWS helper, callback, caching) and helpers to parse/construct providers.
• Filesystem/API:
  • FS read path supports RemoteRef; cache pipeline updates; new SetLogLevel and extended MountOptions (checkpoints, content cache, registry creds).
• Common/Infra:
  • Add gzip/zstd index types, metrics collection, and new storage mode constants.
• Build/Housekeeping:
  • Dockerfile builds all packages; Makefile uses docker build.
• Tests:
  • Extensive tests for OCI format, storage, performance, credentials, and cache behavior.

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