fix(bingads): scope file descriptor cleanup to loop iteration in unzip - #7424

Summary

Fixes file descriptor leaks during zip extraction in Bing Ads audience and offline-conversions utility helpers caused by deferred Close() calls placed directly inside loop iterations.

Root Cause

In Go, defer is evaluated when the surrounding function returns, not when the current loop iteration terminates. In unzip(...) across both audience/util.go and offline-conversions/util.go:

for _, f := range r.File {
    rc, err := f.Open()
    ...
    defer rc.Close()

    file, err := os.OpenFile(...) // or os.Create(...)
    ...
    defer file.Close()
}