Update LLmAgent History API (#146)

* Add persistent history API

* Add ephemeral API for history management

* Formatting

* PR nits

* Moar PR nits

* Validate #process args

Author: akavi

line/llm_agent/__init__.py

@@ -10,6 +10,9 @@
 # Configuration
 from line.llm_agent.config import FALLBACK_INTRODUCTION, FALLBACK_SYSTEM_PROMPT, LlmConfig
 
+# History
+from line.llm_agent.history import History
+
 # LLM Agent
 from line.llm_agent.llm_agent import LlmAgent
 
@@ -31,6 +34,8 @@
 )
 
 __all__ = [
+    # History
+    "History",
     # LLM Agent
     "LlmAgent",
     # Configuration