Increase gRPC message size limits for peerswapd server and REST gateway

[mrfelton]

The /swaps REST endpoint fails with ResourceExhausted errors when responses exceed the default 4 MiB gRPC limit. The server and REST gateway weren't configured with increased limits, unlike the client-side callers which already use 200-500 MiB.

Changes

• Add maxMsgRecvSize constant (500 MiB) to match existing limits in lnd/connect.go and testframework/proxy.go
• Configure gRPC server with MaxRecvMsgSize and MaxSendMsgSize
• Configure REST gateway dial options with MaxCallRecvMsgSize

grpcSrv := grpc.NewServer(
    grpc.MaxRecvMsgSize(maxMsgRecvSize),
    grpc.MaxSendMsgSize(maxMsgRecvSize),
)

opts := []grpc.DialOption{
    grpc.WithTransportCredentials(insecure.NewCredentials()),
    grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(maxMsgRecvSize)),
}

[YusukeShimizu]

Thanks for addressing this.

Instead of raising the gRPC message size limit, how about adding paging (plus minimal filtering if needed) to ListSwaps / ListPeers so responses are bounded by default, since simply increasing the limit hides the symptom but still leaves response size and memory usage growing monotonically as history accumulates.

For backward compatibility, we could either keep the current behavior when paging params are omitted (return all) or introduce a new RPC.