benchmark: align --request_interval_us help text with actual pacing semantics

[Copilot]

Description

--request_interval_us was documented with aggregate semantics that do not match the current implementation. This updates only the flag help text to describe existing per-thread pacing behavior, per the linked review feedback.

• Scope

  • Updated a single user-facing description string in mooncake-transfer-engine/benchmark/utils.cpp.
  • No transfer pacing logic, metrics logic, or control flow changed.

• Behavioral Clarification

  • Previous text: implied a minimum aggregate interval across issued batches.
  • New text: explicitly states per-thread delay before each issued transfer batch.

DEFINE_uint64(request_interval_us, 0,
              "Per-thread delay before each issued transfer batch, in "
              "microseconds. 0 disables pacing.");

Module

• Transfer Engine (mooncake-transfer-engine)
• Mooncake Store (mooncake-store)
• Mooncake EP (mooncake-ep)
• Mooncake PG (mooncake-pg)
• Integration (mooncake-integration)
• P2P Store (mooncake-p2p-store)
• Python Wheel (mooncake-wheel)
• Common (mooncake-common)
• Mooncake RL (mooncake-rl)
• CI/CD
• Docs
• Other

Type of Change

• Bug fix
• New feature
• Refactor
• Breaking change
• Documentation update
• Performance improvement
• Other

How Has This Been Tested?

Test commands:

git diff -- mooncake-transfer-engine/benchmark/utils.cpp
git diff --check

Test results:

• Unit tests pass
• Integration tests pass (if applicable)
• Manual testing done (describe below)

Manual verification confirmed a single-line text-only change with no unintended diffs.

Checklist

• I have performed a self-review of my own code
• I have formatted my code using ./scripts/code_format.sh
• I have run pre-commit run --all-files and all hooks pass
• I have updated the documentation (if applicable)
• I have added tests to prove my changes are effective
• For changes >500 LOC: I have filed an RFC issue

AI Assistance Disclosure

• No AI tools were used
• AI tools were used (specify below)

Used GitHub Copilot Coding Agent to locate the referenced review comment, apply the requested text-only change, and verify the resulting diff scope.