Added provider-level batching for selected arXiv and NCBI operations to reduce unnecessary live-service requests while preserving existing public return shapes.
Added batched NCBI support for PMID, PMCID, and DOI metadata, linked-identifier lookup, existence checks, and supported identifier conversions.
Moved batch execution into the unary and binary dispatch engines so batching is handled consistently through internal dispatchers rather than exported API functions.
Added package-managed throttling for arXiv, NCBI, and Europe PMC requests, with user-configurable rate-limit options.
Added a provider-etiquette vignette documenting batching, throttling, live-service behavior, and relevant user options.