Apply low-pass filter to RTF display

[azeey]

🎉 New feature

Follow-up from https://github.com/gazebosim/gz-sim/pull/1942

Summary

This adds a more aggressive low-pass filter than what was in gz-sim such that the RTF display is more stable and reflects the RTF of a longer window of time.

Test it

Run gz sim camera_sensor.sdf. The RTF will display is much more stable than before. After a while, remove the image display and watch the RTF increase.

Checklist

• [ ] Signed all commits for DCO
• [ ] Added tests
• [ ] Added example and/or tutorial
• [ ] 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.

[azeey]

@iche033 I've made the filter less aggressive than what I had https://github.com/gazebosim/gz-sim/pull/1942 so that it is responsive to changes like the image display being removed while still providing a stable RTF reading.

[codecov[bot]]

Codecov Report

Merging #529 (063b43c) into gz-gui7 (bf42b84) will increase coverage by 0.05%. The diff coverage is 91.30%.

:exclamation: Current head 063b43c differs from pull request most recent head d70596f. Consider uploading reports for the commit d70596f to get more accurate results

@@             Coverage Diff             @@
##           gz-gui7     #529      +/-   ##
===========================================
+ Coverage    69.13%   69.19%   +0.05%     
===========================================
  Files           44       44              
  Lines         4921     4937      +16     
===========================================
+ Hits          3402     3416      +14     
- Misses        1519     1521       +2     

Impacted Files	Coverage Δ
src/plugins/world_stats/WorldStats.cc	94.11% <91.30%> (-0.89%)	:arrow_down:

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