New empty prefix header tests are failing

[adwsingh]

The recent relaxation of the httpPrefixHeaders constraint in Smithy (smithy-lang/smithy#2565) to allow empty prefixes has caused two specific issues in smithy-java:

1. The client request tests now fail because with empty prefix headers, all HTTP headers (including system-generated ones like UserAgent) are bound to the POJO. Since the test requests only specify a subset of headers but use strict equality assertions between the deserialized POJO and test parameters, the tests are failing.

2. The server/client response and server request tests fail because there's a prioritization problem where the code doesn't properly prioritize specific header bindings over prefix header bindings, causing incorrect behavior in the server implementation.