MessageDecoder's initial buffer size should be configurable

MessageDecoder is hard-coded to create a 2 MB buffer for each instance, growing it as necessary. 2 MB is pretty heavy for a request-scoped object, and I've noticed that most of it often goes unused. Can this be configurable with a constructor argument or a system property?

Start by locating MessageDecoder and the code that creates its fixed 2 MB initial buffer. Determine how constructor arguments or system properties are handled in this project, then verify that the initial size can be configured while the existing growth behavior remains intact.

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