Add text segment cache for opened files (#27002)

This PR adds a `TextSegmentCache` for caching opened text segments. This should reduce the amount of time we spend opening the text indexes, which happens many times over the course of all the RPCs. I changed some of the `*_impl` methods to take in an `Arc<TextSegment>` instead of the segment reader and trackers it needs, so some of the fns have more than they need, but that should be fine since we should be loading everything in the second RPC and getting cache hits in subsequent RPCs for the same search query. We won't open the `TextSegment` on the first RPC (number of segments) because we don't pass the storage keys for all the trackers in, and it's probably not worth optimizing because `number_of_segments` is only needed when we are using single segment format.

GitOrigin-RevId: 8f4166206a546a1e9a3130551dfff9e4559c28d9

Author: emmaling27