example: update nidcpower measurement to support multiple instrument sessions

[jayaseelan-james]

• This contribution adheres to CONTRIBUTING.md.

What does this Pull Request accomplish?

Updates the nidcpower_source_dc_voltage measurement to support multiple instrument sessions.

Why should this Pull Request be merged?

Fixes #673.

What testing has been done?

• Verified the measurement execution in InstrumentStudio using individual site values and "All Sites".
• Verified the measurement execution in TestStand using sequential and batch process models.

[github-actions]

Test Results

    30 files  ±0      30 suites  ±0   47m 13s ⏱️ +59s
   639 tests ±0     639 ✅ ±0      0 💤 ±0  0 ❌ ±0 
15 790 runs  ±0  14 730 ✅ ±0  1 060 💤 ±0  0 ❌ ±0 

Results for commit 174a7a3. ± Comparison against base commit 7df2dd8.

♻️ This comment has been updated with latest results.

[dixonjoel]

I'd like you to wait for @bkeryan to review as well.

[jayaseelan-james]

@dixonjoel @bkeryan I've updated the NI-DCPower example fixing the multiple session issue. With this change, the example has become more complex to support multiple instrument sessions. So, I would like to know if this complexity is fine or if we should leave the example as it was earlier and mention this behavior as a comment in the measurement.

Please let me know your thoughts on this.

Edit: The existing example will work with batch process model execution because each test socket would invoke the measure method individually thereby requiring only a single instrument session per execution.

[bkeryan]

Approved with suggestions