Add proxy support to AppStoreServerAPIClient #196
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Summary
This PR adds an optional constructor to AppStoreServerAPIClient that allows users
to provide a custom java.net.Proxy for outbound HTTPS connections.
Motivation
Some developers need to route App Store Server API requests through corporate
proxies or debugging tools (e.g., Charles, Fiddler). This change preserves
backward compatibility while enabling flexible network configuration.
Changes
java.net.Proxy