Implements `IIndexBuilder` interface for BigDeedle. This directly implements operations that can be implemented on virtual vectors (mostly merging, slicing) and for other operations, it calls ordinary `LinearIndexBuilder`. The resulting `VectorConstruction` corresponds to the addressing scheme of the returned index (i.e. if we return virtual, we expect to build virtual vector; if we materialize, the vector builder also has to materialize).

Represents an ordered index based on data provided by a virtual source. The index can be used by BigDeedle virtual frames and series, without accessing all data from the data source. The index only evaluates the full key collection when needed. Most of the actual work is delegated to the `IVirtualVectorSource<'K>` value passed in the constructor.

Represents an ordinal index based on addressing provided by a virtual source. The index can be used by BigDeedle virtual frames and series, without accessing all data from the data source.