Fix long-running example tests in CI

[efaulhaber]

main:

fluid/periodic_array_of_cylinders_2d.jl                   7m59.5s
fsi/falling_rotating_rigid_squares_w_buoys_2d.jl          9m48.3s

This PR:

fluid/periodic_array_of_cylinders_2d.jl                   3m04.2s
fsi/falling_rotating_rigid_squares_w_buoys_2d.jl          3m53.6s

[Copilot]

Pull request overview

This PR reduces runtime for long-running example tests in CI by propagating shortened test parameters and selecting cheaper simulation settings where appropriate.

Changes:

• Overrides the density diffusion model for a fluid example test to use a faster formulation.
• Propagates tspan through the nested FSI buoy example include.
• Updates formatting and attempts to force serial execution for the falling rotating rigid squares example.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
test/examples/examples_fluid.jl	Adds a faster density diffusion override for the periodic cylinder array test.
examples/fsi/falling_rotating_rigid_squares_w_buoys_2d.jl	Passes tspan into the nested base example include.
examples/fsi/falling_rotating_rigid_squares_2d.jl	Reformats several calls and adds a serial backend override to the semidiscretization.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.03%. Comparing base (6bb102a) to head (754ae74).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1227      +/-   ##
==========================================
- Coverage   90.05%   90.03%   -0.02%     
==========================================
  Files         136      136              
  Lines       10594    10595       +1     
==========================================
- Hits         9540     9539       -1     
- Misses       1054     1056       +2     

Flag	Coverage Δ
total	90.04% <ø> (-0.01%)	⬇️
unit	70.77% <ø> (?)

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