[Misc] Refactor benchmark_throughput.py

[lk-chen]

Use named class (instead of tuple) to represent data sample for benchmark

This change makes the code more readable if more fields are added to data sample, e.g. multi-modal data.

This is the first step of #9778, succeeded by #9851

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[comaniac]

Thanks @lk-chen for the great work. Could you briefly explain what this PR does in the description?

Also cc @DarkLight1337 @ywang96

[lk-chen]

Sure, just updated the first comment, PTAL