client: report caller line for OpenStack debug logs

[SAY-5]

What this PR does / why we need it:

The OpenStack API debugger logs every line as client.go:128 regardless of the caller. The wrapper walks the stack with a hard-coded window [10..20] and a substring of /github.com/gophercloud/gophercloud, which no longer spans gophercloud/utils (where the RoundTripper now lives) and fails to reach the real caller through modern net/http frames, so skip stays at 0 and klog.InfoDepth reports its own line.

This walks the whole stack and picks the frame above the deepest /github.com/gophercloud/ frame so klog attributes the entry to the originating call site (e.g. openstack_volumes.go:82).

Which issue this PR fixes(if applicable):
fixes #2300

Special notes for reviewers:
The added test reproduces the bug: it captures klog output via SetOutput while issuing a request through the wrapper and asserts the source location is the test file, not client.go. The test fails on master and passes with this change.

Release note:

Fix OpenStack API debug logs always being attributed to client.go instead of the caller.

[k8s-ci-robot]

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• a710dc8 client: report caller line for OpenStack debug logs

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Hi @SAY-5. Thanks for your PR.

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