feat: add dependency-aware tool execution

[vznh]

Problem

Related to #6399.

Tools returned together currently start in parallel, even when one depends on another. Awaiting the existing executor is insufficient because ctx.update() returns control before the tool finishes.

Behavior

Adds optional local execution ordering:

@function_tool(after=("save_room",))
async def save_meal(ctx: RunContext, meal: str) -> str:
    ...

Independent calls start eagerly. Dependents wait until the function stream closes and all matching prerequisites finish. Tools without dependency metadata retain parallel execution.

• Dependencies apply within one function-stream batch; an absent prerequisite creates no wait. Arguments are not regenerated.
• Progress updates do not satisfy a dependency. Prerequisite errors or individual cancellation do; ordering does not require success.
• Configured name cycles are rejected before dispatch. Session close, stream cancellation, and permanent handoff abandon queued calls while preserving the existing lifetime of admitted session-scoped tools.

Validation

After merging main: 215 focused tests passed, along with make fix, make check, and all executed CI checks on 1ce5bc455.

Coverage includes ordering, progress/result delivery, malformed calls, cancellation, handoff, and provider commit failures. Earlier local unit/audio validation had two baseline process-memory permission failures. Live-provider/evaluation jobs were skipped; live services and physical audio remain unvalidated.

[CLAassistant]

All committers have signed the CLA.

[vznh]

Devin approved ^_^

[vznh]

@tinalenguyen would it be possible to check this over? thank you :-)