Implement a simplified version of STCP functionality.
* **Client Proxy Configuration and Handling**
- Add `STCPProxyConfig` to the `pxyConfs` slice in `client/proxy/general_tcp.go`.
* **Client Visitor Configuration and Handling**
- Add `STCPVisitorConfig` to the `cfg` struct in `client/visitor/stcp.go`.
* **Command Registration and Initialization**
- Add `STCP` to the `proxyTypes` and `visitorTypes` slices in `cmd/frpc/sub/proxy.go`.
* **Configuration Examples**
- Add example configurations for `STCP` proxy and visitor in `conf/frpc_full_example.toml`.
- Add example configurations for `STCP` proxy and visitor in `conf/legacy/frpc_legacy_full.ini`.
* **Configuration Structures**
- Add `STCPProxyConfig` struct and include it in the `proxyConfigTypeMap` in `pkg/config/v1/proxy.go`.
- Add `STCPVisitorConfig` struct and include it in the `visitorConfigTypeMap` in `pkg/config/v1/visitor.go`.
* **Configuration Validation**
- Add validation for `STCPProxyConfig` in `pkg/config/v1/validation/proxy.go`.
- Add validation for `STCPVisitorConfig` in `pkg/config/v1/validation/visitor.go`.
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* support bandwidth_limit set by server plugin
* limiter at proxy level
* bandwidth_limit_mode
* updates tests for bandwidth_limit_mode default
* bandwidth_limit_mode as string
* add checkForSrv for bandwidth_limit_mode
* bandwidth_limit flags for sub cmds
* gci write
The ClientCommonConf, configuration file path, and server UDP port are
now passed around as arguments instead of being shared between
components as global variables. This allows for multiple clients to
exist in the same process, and allows client.Session to be used as a
library more easily.
