feat: drop legacy chat-template-pass-through kwargs (clear_thinking, preserve_thinking)

[hallerite]

Summary

`GLM5Renderer.init` no longer accepts `clear_thinking`, and `Qwen36Renderer.init` no longer accepts `preserve_thinking`. Both were chat-template-kwarg pass-throughs whose default values are now baked straight into the renderer.

Why

These kwargs hung over from when each renderer mirrored the model's Jinja chat-template signature kwarg-for-kwarg. The renderer-agnostic override layer landed in #3 / #5 (`preserve_all_thinking`, `preserve_thinking_between_tool_calls` — constructor-only attributes since #5) subsumes both, and they were the only "non-default" kwarg that the chat-template-pass-through ever needed:

Legacy kwarg	Same as
`clear_thinking=False` (GLM-5)	`preserve_all_thinking=True`
`preserve_thinking=True` (Qwen3.6)	`preserve_all_thinking=True`

Their default values are kept by baking the chat-template behaviour straight in:

• GLM-5: drop `` on past-cycle assistants, keep on in-flight cycle and trailing assistant. (What `clear_thinking=True` did before.) The render gate is now `msg_idx > last_user_index or preserve_thinking` — clean and consistent with the rest of the GLM/Qwen family.
• Qwen3.6: identical to Qwen3.5 (`msg_idx > last_query_index` via the inherited `_should_render_thinking`). The class shrinks to just the `_render_arg_value` override, which is the only real template delta vs Qwen3.5.

Changes

• `renderers/glm5.py`: drop `clear_thinking` constructor kwarg; bake the `True` semantics into the assistant-render gate.
• `renderers/qwen36.py`: drop `preserve_thinking` constructor kwarg and the `_should_render_thinking` override (which existed only to consult `_preserve_thinking`). Class shrinks to `_render_arg_value` only. Module docstring rewritten to call out the simplification.
• `tests/test_preserve_thinking.py`: two new regression tests pinning that the legacy kwargs raise `TypeError` if anyone tries to pass them.
• README: untouched — §1 Preserving past reasoning (constructor-only overrides) (added in feat: bind preserve_*_thinking at construction (drop _bind_preserve_defaults) #5) already motivates the override path; §3.d already cross-links to it for compaction.
• Bump 0.1.9 → 0.1.10.

Test plan

• `pytest tests/` — 895 passed, 48 skipped, 1 xfailed locally (no parity regressions; +2 tests are the new regressions).
• No verifiers / prime-rl downstream impact: neither package ever passed `clear_thinking` or `preserve_thinking` to any renderer constructor — verified by grep.
• Pre-commit / ruff format clean.

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