feat(examples/strands_sglang): update to strands-sglang 0.4.2

[Lawhy]

What

Updates the examples/strands_sglang example to the latest strands-sglang 0.4.2 API.

Changes

• 0.4.2 API migration — read the token trajectory via the new model.rollout (Rollout) tracker instead of the removed model.token_manager: initial_prompt_length for the prompt boundary, plus token_ids / loss_mask / logprobs.
• Self-contained interpreter — the execute_python_code tool now uses an in-example subprocess_interpreter.py, keeping the example dependency-light.
• Deps — remove the one-line requirements.txt (the only extra dependency is strands-sglang, installed directly) and refresh the README install steps.
• Docs — fix the loss_mask / Rollout wording and add a security note that the interpreter runs code with no isolation.

NOTE: subprocess_interpreter.py runs model-generated code in a local subprocess with no isolation — it exists only for the convenience of this example. Use a sandboxed interpreter (Docker, e2b, microsandbox, ...) for anything beyond local experimentation.

Testing

• pre-commit run --files ... (ruff, autoflake, isort, black + file checks) passes on all changed files.
• python -m py_compile passes; the 0.4.2 model.rollout slicing was verified against the installed strands-sglang==0.4.2 + strands-agents==1.26.0.

[Lawhy]

Hi @yitianlian, can you take a look when you have time? This is a simple adaption to the most recent strands-slang version.