Fix undefined timing measurement errors in server context

[thedanhoffman]

Overview

Fix UB issue reported by Valgrind involving timing measurements for prompt processing and eval

Additional information

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: I threw an AI at this, but the fix is simple enough that there's no real downside risk (independently verified this solves the issue)

[thedanhoffman]

Found a few other ones. Moving this draft until those are fixed as well (since this is a pretty small change on its own to merge)

[thedanhoffman]

👀