This PR introduces a cache for GetBlobs request.
The main purpose of this PR is to reduce the getBlobs latency by reading and
decoding blobs from the pool in advance of the actual query. This is important
especially in the context of a sparse blobpool, since it may be necessary to
recover blobs from cells on a getBlobs request.
Previously, the Engine API read and decoded blobs from the pool on every call.
Now those calls check the cache and only fall back to the pool on a miss.
The cache has two modes:
- In topK mode (default), it wakes up periodically, picks the most profitable
pending blob transactions up to the current fork's maxBlobsPerBlock, and loads
their blobs. The selection logic is shared with the miner's block-building
logic. The selection size is derived from eip4844.MaxBlobsPerBlock at the
current head.
- When the CL calls HasBlobs, the cache switches to hasBlobs mode and tries to
pin the set it just reported as available. Cache updates (read, decode, and
optionally conversion in the future) run in background goroutines.
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Co-authored-by: Felix Lange <fjl@twurst.com>
