Cosmos Driver: Validate and Fix Go/ Rust EPK Test Gaps

- The goal is to test that not only is the murmurhash implementation correct, but our encoding is correct as well. We should use the Rust SDKs full PartitionKey -> EPK pipeline, and not just reimplement Go's encoding here. Go's encoding logic SHOULD be the same as Rust's, and Python's, and .NET's, and Java's. That's the intent of this test.

```
let pk = PartitionKey::from(...);
let epk = EffectivePartitionKey::compute(pk);
assert_eq!(baseline_value, epk.as_str())
```
- Add Integration tests for pk_range_cache. It would be good if the cache is filled proactively when creating container client It would also help for removing many of the dead code snippets for this iteration.