1. A computer-implemented method for efficiently extracting contents of container files, at least a portion of the method being performed by a computing device comprising at least one processor, the method comprising: receiving, at a first stage of a file-archiving system, an unnested container file containing a first constituent file and a second constituent file, wherein: the first constituent file is a nested container file that contains the second constituent file; and the file-archiving system is configured to perform a time-consuming file-indexing operation; enabling high file throughput at the first stage of the file-archiving system by refraining, at the first stage of the file-archiving system, from performing the time-consuming file-indexing operation; enabling a second stage of the file-archiving system to perform the time-consuming file-indexing operation on the second constituent file by creating, at the first stage of the file-archiving system, a content hierarchy for the unnested container file that comprises: metadata of the second constituent file; first hierarchical metadata that indicates that the unnested container file contains the nested container file; and second hierarchical metadata that indicates that the nested container file contains the second constituent file; using, at the second stage of the file-archiving system, the content hierarchy to locate the second constituent file within the nested container file; extracting, at the second stage of the file-archiving system, the second constituent file from the nested container file; performing, at the second stage of the file-archiving system, the time-consuming file-indexing operation on the second constituent file.
10. The computer-implemented method of claim 1 , further comprising: after the content hierarchy has been created, receiving a request for the metadata of the second constituent file; locating the metadata of the second constituent file stored within the content hierarchy; responding to the request with the metadata of the second constituent file stored within the content hierarchy.