Improve scans_for_new_key test

[arya2]

Motivation

This test doesn't currently check specific transactions in the results at specific heights. It also doesn't test if Zebra starts scanning for blocks from the start height when it's restarted after a key is registered but before the scan_range() task is finished.

This issue depends on correctly handling ScanTask restarts before a scan_range() task for a newly registered key is finished. See #8238.

Possible Design

• Use ScanService requests to register key and get results instead of ScanTask
• Check for known transaction ids and heights in the test
• Check that it returns scans all of the blocks in the required range when ScanTask restarts before the scan_range() task is finished

[arya2]

Split out adding the test to CI to #8274. The rest of this issue is blocked on handling restarts correctly (See #8238).

[mpguerra]

We won't be doing any more work on the scanner