Raise test coverage to ≥90% (Aone #84428597)

[yndu13]

Summary

• Add unit tests covering DefaultLogger/ClientLogger overloads, LogLevel null, Validate/IOUtils/HostnameVerifier success paths, and Tea helpers (null interceptor chain, toWriteable, interrupted sleep).
• Cover OkHttp CA trust-store setup with bundled test PEMs (no CI CA secret), proxy authenticator callback, and proxy exception paths.
• Extend TeaModel confirmType/parseObject, TeaResponse read failures, OkRequestBody contentLength, and ClientHelper cache-key fields for keepAlive/maxIdle.

[yndu13]

这些证书是否都是假的，如果是真的，不能直接写在代码里。

[yndu13]

确认：原先 PEM 是 CN=test.local 的自签测试夹具，不是生产证书，也未提交私钥。

为消除「真证书入库」疑虑，已删除 src/test/resources/test-ca*.pem，改为单测运行时用 keytool 生成 ephemeral 自签 CA（OU=UnitTestFixture），覆盖路径不变。请 re-review。