feat: use Stringer in getFunctionName when available (ExecuteActivity)

[LukaGiorgadze]

closes #2049

What was changed

• Updated getFunctionName of ExecuteActivity to check if the provided value implements fmt.Stringer.
• If so, it now returns the result of String() directly instead of inspecting the function pointer.
• Existing behavior for raw strings and function pointers remains unchanged.

Why?

• Allows custom types like ActivityName to define their activity names using String().
• Prevents incorrect behavior or panics when passing values that are Stringer but not functions.

Example

type ActivityName string

func (a ActivityName) String() string {
	return string(a)
}

var agentPlannerActivity ActivityName = "AgentPlannerActivity"

fut := workflow.ExecuteActivity(ctx, agentPlannerActivity, inputs{})

Without that, we are encountering an error, and it is difficult to comprehend the underlying reason:

3:22PM INF log/with_logger.go:45 Task processing failed with error Namespace=default TaskQueue=chat-agent WorkerID=28030@Lukas-MacBook-Pro-M4.local@ WorkerType=WorkflowWorker Error="BadScheduleActivityAttributes: ActivityType is not set on ScheduleActivityTaskCommand. ActivityID=15"

Checklist

1. Closes

2. How was this tested:

• Added/ran unit tests to cover:
  • Stringer types (e.g. ActivityName)
  • Plain strings

3. Any docs updates needed?

• No public API change.
• No docs updates required unless internal developer guide references getFunctionName.

[CLAassistant]

All committers have signed the CLA.

[Quinn-With-Two-Ns]

if we do decided to accept this change, I think we would have to check for fmt.Stringer after the function pointer check due to non determinism concerns.

[LukaGiorgadze]

Thank you, updated!