examples: add online SGLang HTTP recipe

[guapisolo]

Summary

• add an online SGLang HTTP example that sends renderer-owned input_ids to /generate
• demonstrate parsing tool calls and bridging a second turn from returned token IDs
• document the source-checkout command path and the PEP 723 package-publish requirement

Verification

• uv run ruff check examples/sglang/online_multiturn_sglang.py
• uv run ruff format --check examples/sglang/online_multiturn_sglang.py
• uv run pytest tests/ -q
• Tested against lmsysorg/sglang:dev serving Qwen/Qwen3.5-4B: both Qwen3.5 thinking modes completed two turns, parsed multiply(17, 23), produced 391, and passed the bridge byte-prefix assertion.