fix(ss): address review findings for PR #96 — nil guards, resource leaks, dead code

- Bump go-shadowsocks2 to v0.1.3 (new API symbols)
- Return error instead of nil when Target() is empty in TCP handler
- Reset wbuf unconditionally on write error to prevent unbounded growth
- Add nil guard on targetAddr before WriteTo to prevent panic
- Remove duplicate NewClientConfig call and dead ClientConfig literal
- Remove unused noDelay metadata field
- Fix buffer-size guard to catch negative values (len(b)==0 → bufSize<=0)
- Add address context to parse/session error messages

connector/ss/metadata.go

@@ -10,19 +10,16 @@ import (
 type metadata struct {
 	key            string
 	connectTimeout time.Duration
-	noDelay        bool
 }
 
 func (c *ssConnector) parseMetadata(md mdata.Metadata) (err error) {
 	const (
 		key            = "key"
 		connectTimeout = "timeout"
-		noDelay        = "nodelay"
 	)
 
 	c.md.key = mdutil.GetString(md, key)
 	c.md.connectTimeout = mdutil.GetDuration(md, connectTimeout)
-	c.md.noDelay = mdutil.GetBool(md, noDelay)
 
 	return
 }