vnav(speed): mach target bug should not be smooth during climb

[tracernz]

Aircraft Version

Development

Build info

{
  "built": "2022-03-03T12:42:13+00:00",
  "ref": "HEAD",
  "sha": "b2d7668d7dcbef695cf7462635c9800234b5967c",
  "actor": "Michael Corcoran <tracer@outlook.co.nz>",
  "event_name": "manual",
  "pretty_release_name": "mrc-how-long-is-a-piece-of:b2d7668d"
}

Describe the bug

From pilot feedback, the mach target is jumps between values while climbing rather than continously sliding on the scale... either it's quantised, or updated at a time interval. Needs some investigation, but opening the issue so I don't forget about it.

Expected behavior

As above.

Steps to reproduce

Climb above the mach switchover point and observe the bug.

References (optional)

No response

Additional info (optional)

No response

Discord Username (optional)

No response

[donstim]

Good to know!

[pinatacolada]

I'm under the impression it is the airspeed that corresponds to the mach number, rounded to the knot. This is also how it is described in FCOM DSC-31-40 AIRSPEED