Previously we were allowing delta-rs to create it own object stores with its own authentication handling. In order to get parity with our existing auth strategy for AWS (which relies on the official aws-config library to get consistency with aws-cli and other AWS tools), we were fetching a token at delta-rs creation time and passing that to the library.

This works for static, long-lived credentials, but fails for dynamically-refreshed credentials like those from IRSA. This PR reworks our use of delta-rs such that we use our own object_store structs, which properly handle credential refreshing.

While debugging this issue, I also discovered that because object_store uses its own HTTP client to make S3 requests (rather than using AWS smithy), there was no token caching being performed, leading to a huge volume of requests to Amazon STS and some additional latency for S3 operations. This PR also introduces our own sophisticated token cache for AWS, with support for lazy and asynchronous token refreshes.