Adds bytesRead() method to RequestContext

[daanjanschouten]

This change exposes bytesRead() on RequestContext for use in application code. The implementation tracks bytes at the I/O layer via an Undertow conduit wrapper, providing accurate measurements with minimal overhead.

The byte count is stored using the existing attachment mechanism, in line with how the existing UNVERIFIED_JWT and FAILURE attachments are used. For requests with empty bodies, Undertow may not create an input conduit, in which case bytesRead() returns 0.

This change is a better version of #2771 because it exposes significantly less API surface area.

After this PR

==COMMIT_MSG==
Adds bytesRead() method to RequestContext
==COMMIT_MSG==

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Description

Adds bytesRead() method to RequestContext

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✨ Features

• Adds bytesRead() method to RequestContext (#2776)