Reduce Copying of RowGroupMetaData and FileMetaData

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

`SerializedFileReader` and friends currently perform a lot of copying of `RowGroupMetadata` and `FileMetadata`, whilst reading indexes and filtering row groups. Neither of these are small or particularly cheap to clone.

**Describe the solution you'd like**

I would like to reduce the amount of unnecessary work being performed, either by altering the interfaces so data can be moved instead of cloned, or using Arc

**Describe alternatives you've considered**

**Additional context**

Start by tracing SerializedFileReader and related readers through index loading and row-group filtering. Inspect where RowGroupMetadata and FileMetadata are cloned, then evaluate whether ownership changes or Arc can avoid unnecessary copies. Done means reducing redundant metadata copying without changing reader behavior, with relevant tests still passing.

Written by the indexing model from the issue text.