Fix steady state callback interval handling

[svchb]

Summary

• respect interval before evaluating the steady-state kinetic-energy condition
• normalize integer tolerances to floating-point values so the callback can be constructed with integer inputs
• reject non-positive interval_size values

Root Cause

The discrete callback condition called steady_state_condition! directly, so interval was never checked. The constructor also chose the previous kinetic-energy vector element type before converting tolerances to a floating type, which made integer tolerances try to store Inf as an integer.

Validation

• julia --project=. -e 'using Test, TrixiParticles; include("test/callbacks/steady_state_reached.jl")'

[codecov]

Codecov Report

❌ Patch coverage is 97.22222% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.04%. Comparing base (8780b50) to head (fd83a59).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
test/callbacks/steady_state_reached.jl	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1180      +/-   ##
==========================================
+ Coverage   90.00%   90.04%   +0.03%     
==========================================
  Files         135      136       +1     
  Lines       10569    10594      +25     
==========================================
+ Hits         9513     9539      +26     
+ Misses       1056     1055       -1     

Flag	Coverage Δ
total	90.05% <97.22%> (+0.03%)	⬆️
unit	70.76% <83.33%> (+0.05%)	⬆️

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[efaulhaber]

/run-gpu-tests