feat: support mieru protocol

[enfein]

update #1697

[wwqgtxx]

We found a problem. After mihomo released v1.19.0, many embedded users requested to exclude mieru due to the greatly increased binary size.

As the conclusion of the investigation, github.com/enfein/mieru/v3/apis/client should not rely on the top-level package github.com/enfein/mieru/v3/pkg/appctl. In fact, client only calls appctl's FlatPortBindings and ValidateClientConfigSingleProfile, but this will force downstream projects to rely on the complete google.golang.org/grpc and increase the binary size by about 7mb on mainstream platforms.

In mihomo's use case, it makes no sense to include the google.golang.org/grpc, but the import of the top-level package of appctl causes the golang compiler to be unable to determine that this part of the code is unreachable. In a personal test, moving these two functions to a separate subpackage and only importing this subpackage in the client can make mihomo no longer rely on google.golang.org/grpc after executing go mod tidy, and greatly reduce the compilation size.