Update balancers to comply with the breaking change in google.golang.org/grpc@v1.74.0

[tokongs]

I can't upgrade the grpc library in our project because these balancer no longer implement the balancer.Balancer interface with the newest version of grpc.

The balancers need to implement the ExitIdle() method.

[tstirrat15]

Do you have documentation on that method? I'm not familiar enough with that part of gRPC.

[tstirrat15]

Looking around: grpc/grpc-go#8345

GoogleCloudPlatform/grpc-gcp-go#116

Looks like a no-op is sufficient unless we want something special. @tokongs would you be willing to put up that PR?

[tstirrat15]

Okay, that's merged and release. Can you close this if it fixes your issue?

[tokongs]

Haven't tested, but I'm positive it will fix the issue! Thanks for the help:)