feat(dag-protobuf): cache dag pb directory structure and block indexes

[fforbeck]

Context

The requests to fetch a DAG Protobuf directory structure using a CID execute the following steps:

1. Get all content claims lookups to identify where we are pulling data from
2. Fetch cid bafy...cid - which represents the folder containing the target file, so that we can determine the verifiable cid for the file (let's call that bafy...file)
3. Fetch cid bafy...file to get the root block of the file, which in UnixFS contains NO raw data, but rather is a list of sub-blocks that contain the file (let's call those bafy...bytes1 and bafy...bytes2)
4. Fetch the first raw data blocks to send the first byte

This PR enables the caching strategy for steps 2 to 4 where instead of fetching the directory structure from the locator and navigating the DAG for every request, it caches the DAGs if they have a Protobuf structure and content size <= 2MB.

Changes

• Updated withContentClaimsDagula middleware to cache DAG PB content requests
• New KV Store
  • DAGPB_CONTENT_CACHE
• Caching rules
  • FF_DAGPB_CONTENT_CACHE_TTL_SECONDS: The number that represents when to expire the key-value pair in seconds from now. The minimum value is 60 seconds. Any value less than 60MB will not be used. We will use 5 minutes TTL by default.
  • FF_DAGPB_CONTENT_CACHE_MAX_SIZE_MB: The maximum size of the key-value pair in MB. The minimum value is 1 MB. Any value less than 1MB will not be used. We will use 2MB max file size by default.
  • FF_DAGPB_CONTENT_CACHE_ENABLED: The flag that enables the DAGPB content cache. The cache is disabled in prod by default.

Samples

2MB file - no cache

• 5.2 seconds

2MB file - cached

• 1.4 seconds

KV Limits

• Reads: unlimited
• Writes (different keys): unlimited
• Writes (same key): 1w / sec (rate limiting)
• Storage/account & Storage/namespace: unlimited
• key size: <= 512 bytes
• value size: <= 25MiB
• Minimum cache ttl: 60 seconds
• Higher limit? -> https://forms.gle/ukpeZVLWLnKeixDu7

resolves storacha/project-tracking#301