Batch reading content files to prevent `too many open files` error #12079

We shouldn’t need to do this for our Rust code because it utilizes Rayon’s default thread pool for parallelism. This threadpool has roughly the number of cores as the number of available threads except when overridden. This generally is much, much lower than 500 and can be explicitly overridden via an env var to work around potential issues with open file descriptors if anyone ever runs into that.