sdk/go/v0.18.0

NOTE: These notes are inclusive of all preview releases in the v0.18.0 series.

Related to new Modus agents feature:

• feat: initial implementation of Modus Agents #840
• feat: persistence and lifecycle improvements for Modus Agents #843
• fix: correct agent base event stubs #848
• chore: rename agent lifecycle methods and APIs #858
• feat: add agent management APIs #866
• feat: stream agent events via subscriptions #875
• fix: address agent lifecycle issues #881
• feat: add kubernetes secrets provider and API to read secrets #885
• fix: default send message to have no timeout #896

Other items:

• fix: omit parallel_tool_calls in Go OpenAI SDK if it is set to true #849
• feat: add functions for parsing chat messages #853
• feat: enforce WASI reactor mode #859
• feat: return user and chat errors in API response #863
• feat: delete collections features #872