fix(packaging): handle Windows binary extension (.exe) in manifest.json and packaging script

[ZhuchkaTriplesix]

Summary

Fixes entry point mismatch when packaging clickhouse-query-ext for Windows targets.

Closes #45

Changes

• In scripts/package_qext.sh, when packaging for Windows (*windows* target or .exe binary), dynamically update the staged manifest.json so that main specifies bin/clickhouse_rpc_server.exe.
• In the staging directory, copy the binary as both clickhouse_rpc_server.exe and clickhouse_rpc_server for dual backward compatibility across POSIX tools and Windows installer validation in Querya Desktop (ExtensionSupport.validateDriverPackage and ExtensionDriverSession).
• Verified packaging for both Linux and Windows targets; confirmed manifest.json within the archive correctly points to bin/clickhouse_rpc_server.exe on Windows.