TaskManager: reset() during nesting can corrupt the concurrency counter

TaskManager: タスクに weight を持たせて concurrency を「重みの合計」で制御したい

TaskManager: queue で待機中のタスクの優先度を時間経過で自動昇格 (aging) させたい

Return concatinated result when streaming is enabled

Add support for `tool_choice` for Gemini

Add support for multiple function calling for Gemini

Add support for structured outputs for Gemini

After `yarn run build`, `git status` shows some Untracked files

`geminiAgent` failed by `models/gemini-1.5-flash is not found`

`yarn run test` causes test failures