AKD Task: Pydantic AI Base Agent

[sanzog03]

Create a Pydantic AI base agent that support interface from AKD core.

[sanzog03]

A draft pr that implements the pydantic AI runtime in addition to openAI sdk, called PydanticAIBaseAgent in NASA-IMPACT/akd-ext#74

[sanzog03]

The class diagram that showcases the implementation, which is in sort, extension of pydanticAI.Agent and implementation of AKDAgent Protocol.

[sanzog03]

I have broken down the pr: #74 is branched out of develop, and all other addons are branched out of #74. The structure looks like this.

#74  base pydantic  (PydanticAIBaseAgent runtime — arun/astream,
                      tool adapter, event translator, Hooks-based
                      RunContext capture via pai_run_context extra)
   │
   ├── #77  RunContext for backward compatibility
   │        (_context_adapter.py — reflects pai messages/usage/run_id
   │         onto AKD RunContext typed fields; existing apps that read
   │         run_context.messages / .usage keep working)
   │
   ├── #78  tool call limit
   │        (ToolCallLimits capability — caps max_tool_iterations /
   │         max_tool_calls; raises UsageLimitExceeded subclasses)
   │
   ├── #79  reflection capability
   │        (ReflectionCapability — injects reflection_prompt as
   │         SystemPromptPart on every model request after the first)
   │
   ├── #81  history trimmer
   │        (make_ratio_trimmer — stateless ratio-based message
   │         trimmer; history_processors config field; opt-in via
   │         enable_trimming, off by default)
   │
   └── #82  reasoning / thinking capability
            (reasoning_effort → pydantic_ai.capabilities.Thinking —
             turns on the model's reasoning / extended-thinking mode
             at the configured effort level; no-op on non-reasoning
             models)

##  Links:
  - #74 — base pydantic: NASA-IMPACT/akd-ext#74
  - #77 — RunContext for backward compatibility: NASA-IMPACT/akd-ext#77
  - #78 — tool call limit: NASA-IMPACT/akd-ext#78
  - #79 — reflection capability: NASA-IMPACT/akd-ext#79
  - #81 — history trimmer: NASA-IMPACT/akd-ext#81
  - #82 — reasoning / thinking capability: NASA-IMPACT/akd-ext#82

PS: the documentation resides in #74 and has not ben changed, and will update after the closure of all addon prs.