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

go.sum

@@ -51,8 +51,8 @@ github.com/gin-gonic/gin v1.10.1 h1:T0ujvqyCSqRopADpgPgiTT63DUQVSfojyME59Ei63pQ=
 github.com/gin-gonic/gin v1.10.1/go.mod h1:4PMNQiOhvDRa013RKVbsiNwoyezlm2rm0uX/T7kzp5Y=
 github.com/go-gost/core v0.4.0 h1:jLuIMO7ZMJX/BDCYLrYXAmIykT+HkqEuzaTeLMdrY1c=
 github.com/go-gost/core v0.4.0/go.mod h1:WGI43jOka7FAsSAwi/fSMaqxdR+E339ycb4NBGlFr6A=
-github.com/go-gost/go-shadowsocks2 v0.1.2 h1:qgTUQS6aCGzsFArjiKjLP0a7zEVtEYVCRVc5LjOsaVk=
-github.com/go-gost/go-shadowsocks2 v0.1.2/go.mod h1:866zFNNI3He6Wef1M/IvAjTal74WhcfKfBgRpTlkKys=
+github.com/go-gost/go-shadowsocks2 v0.1.3 h1:6CUZLp+mTWXnKP2aK8/Z9ZP+ERMX9gSbywmPu4kGX/A=
+github.com/go-gost/go-shadowsocks2 v0.1.3/go.mod h1:866zFNNI3He6Wef1M/IvAjTal74WhcfKfBgRpTlkKys=
 github.com/go-gost/gosocks4 v0.1.0 h1:eAzev6qw4fzkFQKC9uCHLVNnnPdHyqCggbnfNN80Pmk=
 github.com/go-gost/gosocks4 v0.1.0/go.mod h1:hzVjwijJuZR1pp3GqpTj+AKcSGrx68RlWTrQMFMYBP0=
 github.com/go-gost/gosocks5 v0.5.0 h1:YE37l1MJwde8diIQdynStqogMotG5enoTdborhA5yic=