fix(importer): close REST response body on HTTP error

[keeltrace]

Overview

Close the REST source response body before returning an HTTP status error from restSourceRecord.Open.

Fixes#5985

Details

Open returns resp.Body to callers on success, but previously returned early on 4xx/5xx responses without closing it. This closes the body on the error path and adds a regression test using a tracking ReadCloser.

Testing

• go test -v ./internal/importer -run 'TestRestSourceRecord_Open'
• go test ./internal/importer
• git diff --check

AI-assisted contribution: I used an AI coding agent during investigation and implementation. I reviewed the final diff and ran the verification listed above. I am responsible for the submitted change and follow-up.

[michaelkedar]

/gcbrun

[michaelkedar]

Thanks, happy to merge if you could fix the lint error

[michaelkedar]

/gcbrun

[keeltrace]

Ty!