Test the (q,) NeuralNetworkIntegrator iterate method

[michakraus]

Summary

#308 rewrote the signature of the iterate method for a NeuralNetworkIntegrator on (q,) initial conditions, but no test called that method, so codecov/patch on #308 reported 0% of the diff covered. This PR adds one assertion to the "Layer and architecture docstring examples" testset: the docstring's ResNet, run from (q = [1, 1, 1],) for four points, must return (q = [1 2 4 8; 1 3 9 27; 1 3 7 15],).

The expected trajectory is the closed form of x ↦ x + Wx + b with W = diag(1, 2, 1), b = (0, 0, 1), not a recomputation. A CHANGELOG entry is under [Unreleased] → Added.

The branch name is the one #308 used: its commits are already in main, and against main this PR is the test and its CHANGELOG line only.

Pre-PR verification

Fixed: the missing CHANGELOG entry for the new test.

Unresolved: none.

Pre-existing, not in this diff (nits):

• The iterate docstring in src/architectures/neural_network_integrator.jl gives the example ResNet as x ↦ Wx + b. The network computes x + Wx + b, which the doctest output and both tests show: nn([1, 1, 1]) == [2, 3, 3], not [1, 2, 2].
• The same docstring describes ics as "a NamedTuple of two vectors", but its example passes a vector.

Checked and clean:

• Correctness: which(iterate, …) for a (q = Vector,) argument resolves to the (q,) method. The testset passes 5/5 on Julia 1.13.0 and 1.14.0-DEV.3309.
• Type piracy: the diff adds no method. Aqua.test_piracies reports the 3 known methods in src/layers/resnet.jl that test/aqua.jl asserts.
• Type stability: the covered call infers @NamedTuple{q::Matrix{Int64}}.
• Allocations: fatou lint is clean on the changed file, and the hunk has no allocating construct.
• Comments and history: the hunk adds no comment and no historical prose.
• Formatting: JuliaFormatter (sciml) passes on the changed file.

Not checked: the 1.10 LTS floor (CI's min job covers it), a docs build (no docs or docstring change), and the full suite (left to CI).

🤖 Generated with Claude Code

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.14%. Comparing base (4a9b4c4) to head (f192483).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #309      +/-   ##
==========================================
+ Coverage   86.07%   86.14%   +0.06%     
==========================================
  Files          76       76              
  Lines        3016     3016              
==========================================
+ Hits         2596     2598       +2     
+ Misses        420      418       -2     

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