PubChem SMARTS target-index shards

Persisted smarts-rs target-index shards built from the PubChem CID-SMILES corpus. The archive contains 9 zstd-compressed epserde shard files covering 123857298 target records, one zstd-compressed target-SMILES sidecar per shard, one zstd-compressed external-ID sidecar per shard, and a JSON manifest. Decompress the .eps.zst, .target-smiles.eps.zst and .external-ids.eps.zst files before mmap-backed querying.