SSL_CERT_DIR containing multiple directories not supported

### Describe the bug

Currently Copilot Cli is not OpenSSL compliant in handling of environment variable `SSL_CERT_DIR`.

### Affected version

GitHub Copilot CLI 1.0.59

### Steps to reproduce the behavior

1. Set `SSL_CERT_DIR` to a path containing multiple directories separated by colons, e.g. `/home/username/.aspnet/dev-certs/trust:/usr/lib/ssl/certs`
2. Start GitHub Copilot Cli `copilot`
3. Error message is thrown:
> Cannot open directory /home/username/.aspnet/dev-certs/trust:/usr/lib/ssl/certs to load OpenSSL certificates.

### Expected behavior

Copilot conforms to OpenSSL documented behavior with regards to environment variables `SSL_CERT_DIR` and `SSL_CERT_FILE`, see [openssl-env - OpenSSL environment variables](https://docs.openssl.org/3.0/man7/openssl-env/) for reference

### Additional context

Official [.NET SDK](https://github.com/dotnet/sdk) recommends setting `SSL_CERT_DIR` to multiple directories, in order to trust the local developer certificate.

找出讀取 SSL_CERT_DIR 和 SSL_CERT_FILE 的 CLI 程式碼，然後將其行為與所參照的 OpenSSL 環境變數文件進行比較。使用以冒號分隔的範例重現問題，並確認可以處理多個憑證目錄，同時維持現有的單一目錄行為不變。

由索引模型根據 Issue 內容生成。