Add checksum listeners before response targets

[mullermp]

Fixes #3244

This approach simply emits the chunk data prior to writing it out to the body. When emitting, the chunk may be modified, then that modified chunk may be written to the body. Checksum verification relies on on_data to verify chunks of data. Checksum verification fails when the chunk is mutated.

Initially tried a different approach of moving moving checksum response listeners to be very early in the stack (listeners are executed in the order that they are registered) and changing the listeners to use on_data instead of on_headers, but this had issues because on_data would re-register bodies each time and had issues with client encryption.

[github-actions]

Detected 1 possible performance regressions:

• aws-sdk-cloudwatchlogs.require_time - z-score regression: 3.32 -> 13.6. Z-score: 22.67

[jterapin]

Nice, looks fine. I added some minor alignment suggestions so that it's easier to resolve it here.

[alextwoods]

Nice - approach makes sense.