Small vectors in various sizes. These store a certain number of elements inline, and fall back
to the heap for larger allocations. This can be a useful optimization for improving cache
locality and reducing allocator traffic for workloads that fit within the inline buffer.
Shareable script_pubkey for UTXO: small scripts use inline storage; longer use Arc<[u8]>.
Clone is cheap (inline copies up to 64 bytes, shared is Arc::clone). Serde matches ByteString.
Pre-allocate a UtxoSet for n entries. Avoids costly reallocation spikes when loading large
checkpoints (at 50M entries the HashMap table alone is ~2.5 GB; a growth-triggered realloc
temporarily doubles that).