gz_TEST: improve initial sim time test reliability

[scpeters]

🦟 Bug fix

Improves reliability of a test added in #1801.

Summary

The test added in #1801 is a little flaky:

• https://build.osrfoundation.org/job/ignition_gazebo-ci-gz-sim7-homebrew-amd64/66/testReport/junit/(root)/CmdLine/SimtimeArgument/

I've added delays, which wasn't enough on its own. For some reason the test subscriber on macOS doesn't get any messages for the first 100 iterations or so. Increasing to 200 iterations was enough in most cases on my machine, so I increased to 500 just to be safe. To reproduce the issue, reduce the iterations to 100 and view the console output.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #1916 (e569d3f) into gz-sim7 (753ec8d) will increase coverage by 0.06%.
The diff coverage is 85.29%.

❗ Current head e569d3f differs from pull request most recent head d238274. Consider uploading reports for the commit d238274 to get more accurate results

@@             Coverage Diff             @@
##           gz-sim7    #1916      +/-   ##
===========================================
+ Coverage    64.54%   64.61%   +0.06%     
===========================================
  Files          347      348       +1     
  Lines        27777    27853      +76     
===========================================
+ Hits         17930    17997      +67     
- Misses        9847     9856       +9     

Impacted Files	Coverage Δ
include/gz/sim/components/Component.hh	100.00% <ø> (ø)
src/gui/plugins/spawn/Spawn.cc	9.88% <0.00%> (-0.40%)	⬇️
include/gz/sim/components/Factory.hh	97.16% <95.74%> (-0.37%)	⬇️
src/ComponentFactory.cc	100.00% <100.00%> (ø)
src/systems/physics/Physics.cc	67.22% <100.00%> (+0.87%)	⬆️

... and 2 files with indirect coverage changes

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[scpeters]

still flaky; it failed in one of the jammy actions:

• https://github.com/gazebosim/gz-sim/actions/runs/4334098080/jobs/7567757268

[azeey]

Since the loaded sdf file has some plugins, none of the more time consuming plugins such as Physics are loaded. Also, the plugins.sdf world is set to run as fast as possible, so this command may finish running before transport is done initializing. My suggestion is to slow it down using -z 1000 or even -z 100.

[azeey]

d238274

[azeey]

The ABI failure is because there are new changes in gz-sim7 since this was last updated. Since it's pretty clear this doesn't actually break ABI, I'll go ahead and merge.