ACU Agent: generate_scan waits for settling, before exiting

[mhasself]

Description

After it stops uploading points, generate_scan waits for the az to settle at (a) the last commanded position and (b) at velocity zero. Once those conditions are met, the process exits. Previously there was just a flat 10 second wait. There were cases observed where this wasn't long enough.

This does break fromfile_scan. Sorry. That's not used in observations but it's useful so I will get it working again, soon.

Motivation and Context

Resolves a crash seen on SAT where a scan ends, and immediately a new Preset position is commanded (while ProgramTrack is still settling down); the ACU seems to get confused and approach the new target very slowly, which times out the go_to state progress checker.

How Has This Been Tested?

Tested extensively on simulator and also on SATP3 just now. Behaves as desired.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[BrianJKoopman]

Looks good to me, just one small question and a request to open an issue for the broken task. Going to go ahead and merge.