[DYNAMO] add chat nvext transport

[AmeenP]

Summary

Adds the Dynamo token-in wire shape to the standalone renderers package, which is now the canonical home for renderer client code.

• adds RendererTransport = Literal["prime_vllm_generate", "dynamo_chat_nvext"]
• keeps the existing vLLM /inference/v1/generate behavior as the default
• adds dynamo_chat_nvext, posting placeholder chat messages plus nvext.token_data and stop_token_ids to /chat/completions
• reads completion token IDs from Dynamo's token_ids / nvext.completion_token_ids response locations
• exports the transport type from renderers.__init__

Context

This replaces the old verifiers PR path that edited packages/renderers/...; latest verifiers/main now depends on the standalone PrimeIntellect-ai/renderers repo.

Paired stack:

• PrimeIntellect-ai/verifiers#1287
• PrimeIntellect-ai/verifiers#1313
• PrimeIntellect-ai/prime-rl DYNAMO stack
• ai-dynamo/dynamo#9131

Validation

• uv run ruff check renderers/client.py renderers/__init__.py tests/test_client.py
• uv run ruff format --check renderers/client.py renderers/__init__.py tests/test_client.py
• python -m py_compile renderers/client.py renderers/__init__.py tests/test_client.py

uv run pytest tests/test_client.py exited 139 on the local macOS/Anaconda environment before pytest output; relying on Linux CI for the pytest run.