Freeze SBIG TEC during readout to reduce noise, per spec

What is the purpose of this Pull Request?

Some users are reporting banding in their SBIG images. Some investigation revealed this happens only when the TEC is enabled, and I found an obscure bit in the documentation that reveals the need to “freeze” the TEC during readout.

How were the changes tested?

Affected user tried a private build and confirmed the issue goes away.

Did all Unit Tests pass?

Yes

Are there relevant Issues in the tracker that this PR will fix?

Screenshots

Notes