Fixes for ResponsesState state.rs

[praxis-bot]

• state.rs:11 and :20 - Broken rustdoc links to crate::extensions::RequestExtensions; update to point to the actual module path from PR feat(filter): add RequestExtensions type-map for request-scoped state #621 once it merges, or use a plain-text reference until then.
• state.rs:117 - request_body field initializer is listed last in Self { .. } but appears earlier in the struct definition. Reorder initializers to match declaration order per project conventions.
• state.rs:182 - extract_u32 silently drops unparseable max_tool_calls values (negative, float, overflow) without logging, which could mask malformed requests that fall back to unlimited agentic loop iterations. Add a tracing::debug! when a value is present but unparseable.

Follow-up from #635 (review)