The slot parameter in blobCacheEntry.filter was unused and redundant.
All slot/epoch-sensitive checks happen before filter
(commitmentsToCheck), and disk availability is handled via
BlobStorageSummary (epoch-aware).
Changes:
- Drop slot from blobCacheEntry.filter signature.
- Update call sites in availability_blobs.go and blob_cache_test.go.
Mirrors the data_column_cache.filter API (which does not take slot),
reduces API noise, and removes dead code without changing behavior.
