feat: add multi-image latency benchmarking

[sjarvie]

Summary

Add benchmarking capability to measure latency impact of multiple images (frames) per request in GuideLLM. This enables testing how TTFT and ITL scale with multi-frame vision inputs.

• Schema: New MultiImageDatasetConfig extending synthetic data generation with images_per_request parameter
• Generator: 720p synthetic image generation with base64 encoding and reproducible seeding
• CLI: New --images-per-request parameter supporting single or comma-separated values (e.g., 1,2,5)
• API: MultiImageBenchmark programmatic class for pytest integration

Test Plan

• 6 unit tests for config validation (bounds, inheritance, defaults)
• 8 unit tests for image generator (encoding, reproducibility, dimension accuracy, pixel/byte tracking)
• All 14 tests passing with proper assertions on JPEG format and base64 validity

Implementation Details

Files Created:

• src/guidellm/data/schemas.py — MultiImageDatasetConfig
• src/guidellm/data/generators/multi_image.py — Image generator (720p)
• src/guidellm/data/generators/__init__.py — Module exports
• src/guidellm/benchmark/multi_image.py — Programmatic API
• tests/unit/data/test_multi_image_config.py — Config validation tests
• tests/unit/data/generators/test_multi_image_generator.py — Generator tests

Files Modified:

• src/guidellm/data/deserializers/synthetic.py — MultiImageDatasetConfig support
• src/guidellm/cli/benchmark/run.py — CLI parameter
• src/guidellm/benchmark/__init__.py — API exports
• docs/getting-started/benchmark.md — Usage guide with examples

Usage Examples

CLI (single image count):

guidellm benchmark --target http://localhost:8000 --images-per-request 2 --profile constant --rate 10

CLI (multi-variant):

guidellm benchmark --target http://localhost:8000 --images-per-request 1,2,5 --profile constant --rate 10 --max-seconds 30

Programmatic:

from guidellm.benchmark import MultiImageBenchmark

bench = MultiImageBenchmark(image_counts=[1, 2, 5], prompt_tokens=256)
configs = bench.get_configs()  # {1: config, 2: config, 5: config}

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @sjarvie.

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @sjarvie.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mergify]

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