Add support for parallel tool calls

[myakhnis-siro]

Describe the solution you'd like

• ADK Python allows for parallel tool calls, a big performance boost when considering LLM interpretation steps between each tool call.
• It'd be great to support this in adk-js as well.
• Currently, every tool call is sequential.

[Varun-S10]

Hi @myakhnis-siro, We appreciate you taking the time to share your thoughts with us, and we'll be filing a feature request.

Hi @sasha-gitg , I would like to escalate user request to add parallel tool calling in TypeScript, matching what is currently available in Python.