test: add unit tests for openai_llm2_python ThinkParser

[nuthalapativarun]

Summary

• Add 16 unit tests for ThinkParser in openai_llm2_python, covering the <think>...</think> reasoning-block parser used to handle streaming LLM responses from reasoning models (e.g. o1, DeepSeek-R1 style)
• Add conftest.py that stubs ten_runtime and ten_ai_base so pure-Python helper tests run without a full TEN runtime installation
• No changes to production code

What is tested

Test	Coverage
test_plain_text_produces_message_delta	Normal text emits message_delta
test_think_block_produces_reasoning_events	Full block emits reasoning_delta + reasoning_done + message_delta
test_think_block_reasoning_content	Correct content in delta/done events
test_message_after_think_block	Text after </think> emitted as message_delta
test_empty_input_returns_no_events	Empty string → no events
test_partial_open_tag_buffered	Trailing <th is held in _pending
test_partial_open_tag_resolved_on_next_chunk	Pending prefix flushed when next chunk rules out <think>
test_split_think_tag_across_chunks	<thi / nk> split across calls still detected
test_state_returns_to_normal_after_think	State machine resets after </think>
test_finalize_flushes_pending_normal	finalize() drains _pending in NORMAL state
test_finalize_closes_open_think_block	finalize() closes unclosed THINK block
test_multiple_think_blocks	Two back-to-back blocks both produce reasoning_done
test_process_reasoning_content_emits_delta	process_reasoning_content() path
test_process_reasoning_content_empty_closes_block	Empty string closes THINK state
test_process_returns_false_for_plain_text	Legacy process() bool return
test_process_returns_true_on_state_change	process() returns True on state transition

Test plan

• python3 -m pytest ai_agents/agents/ten_packages/extension/openai_llm2_python/tests/ -v — 16/16 passed
• task format — clean (no production code changes)