pingora-core brings in tokio's test-util feature flag

## Describe the bug

pingora-core is transitively bringing in tokio's test-util feature flag by depending on tokio-test.

This is problematic because tokio's implementation changes in many places if the test-util feature is turned on. For example, tokio's Instant::now implementation is changed and is less performant.

## Pingora info

Please include the following information about your environment:

**Pingora version**: 0.4.0
**Rust version**: 1.86.0
**Operating system version**: N/A

## Steps to reproduce

Create a crate that depends on pingora 0.4.0.

Via cargo tree, you can see the tokio test-util feature is included:
`cargo tree --edges features --edges normal --invert tokio`

## Expected results

I expect tokio's test-util feature to not be included by default.

## Observed results

tokio's test-util feature is included in pingora's dependency closure.

## Additional context

None