fix(ai): Fix fraction seconds bug with ProtoDuration

[daymxn]

This PR fixes a minor bug I came across in the ProtoDuration decoding. It's not a emergency release worthy bug, but it can produce an incorrect nanosecond value (ie; instead of 123000000 it currently produces 123). In practicality, this means that within LiveServerGoingAwayNotice, the timeLeft field could be off by +-1 second.

Tests have been added for ProtoDuration as well, to help avoid this in the future.

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[ncooke3]

/gemini review

[gemini-code-assist]

Code Review

This pull request correctly fixes a bug in ProtoDuration decoding where the fractional part of a second was misinterpreted. The addition of unit tests is also a great improvement to prevent future regressions. My review includes a suggestion to use Decimal instead of Double for the nanosecond calculation to make it more robust against floating-point inaccuracies. I've also added some minor suggestions to improve the new tests by specifying accuracy for floating-point comparisons.