Handle raw output for sequences without ADC

[cncastillo]

Problem

simulate(...; sim_params["return_type"] = "raw") failed for sequences without ADC samples because raw-data conversion tried to reduce an empty k-space trajectory and show assumed at least one profile.

Solution

Returns a header-only RawAcquisitionData when no ADC events are present and makes show handle empty profile lists.

Tests

• Pkg.test("KomaMRICore")

Development

Closes #165

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.70%. Comparing base (3a2aad0) to head (808b5a7).
⚠️ Report is 27 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #763      +/-   ##
==========================================
- Coverage   89.66%   88.70%   -0.97%     
==========================================
  Files          74       74              
  Lines        5179     5180       +1     
==========================================
- Hits         4644     4595      -49     
- Misses        535      585      +50     

Flag	Coverage Δ
base	86.48% <ø> (ø)
core	80.72% <100.00%> (-7.29%)	⬇️
files	95.26% <ø> (ø)
komamri	88.23% <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	98.75% <100.00%> (+1.52%)	⬆️

... and 6 files with indirect coverage changes

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