Reject negative ADC labels and default raw recon to custom

[cncastillo]

Problem

Negative ADC labels fail late during raw-data conversion because ISMRMRD encoding counters are unsigned. For long simulations this means users only see the failure after simulation work has already completed.

The raw-data header also used other as the default trajectory label, while KomaMRI-generated raw data should use custom for reconstruction.

Solution

• Checks cumulative ADC labels with get_labels(seq) at the start of simulate and stops on the first negative value.
• Changes the raw-data trajectory default from other to custom.
• Updates the label tutorial to start from the default zero counter instead of using a negative LabelSet hack.

Tests

• Pkg.test("KomaMRICore")

Development

Closes #637
Context: discussion #786

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.57%. Comparing base (230fbad) to head (25233f3).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #765      +/-   ##
==========================================
- Coverage   89.82%   88.57%   -1.26%     
==========================================
  Files          76       76              
  Lines        5398     5399       +1     
==========================================
- Hits         4849     4782      -67     
- Misses        549      617      +68     

Flag	Coverage Δ
base	86.47% <ø> (ø)
core	79.76% <100.00%> (-9.89%)	⬇️
files	95.26% <ø> (ø)
komamri	88.32% <ø> (ø)
plots	90.88% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
KomaMRICore/src/rawdata/ISMRMRD.jl	98.59% <ø> (+1.36%)	⬆️
KomaMRICore/src/simulation/SimulatorCore.jl	90.28% <100.00%> (-0.42%)	⬇️

... and 6 files with indirect coverage changes

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[cncastillo]

CI failed in the docs build because examples/3.tutorials/lit-07-label.jl used the old LabelSet(-1, "LIN") offset trick before simulation. This branch now assigns explicit zero-based nonnegative LIN values on ADC blocks, so the validation remains strict and the tutorial still feeds MRIReco zero-based lines.

Verified locally with julia --project=docs docs/make.jl.

[cncastillo]

Follow-up: the tutorial now uses the intended LabelInc form instead of explicit LabelSet values. Label counters already start at 0; the increment is attached to the block after each ADC, so ADC profiles read 0, 1, 2, ... without ever creating a negative label state.

Verified with julia --project=docs docs/make.jl.