Add dwidenoise2 denoising option

[tsalo]

Closes #1070.

Changes proposed in this pull request

• Add dwidenoise2 as a --denoise-method option, with a DWIDenoise2 interface and the corresponding Dockerfile build (dwidenoise2, dwi2noise, and the bundled noise-estimation schedules).
• Allow --denoise-method to take semicolon-delimited parameters, e.g. dwidenoise2;estimator:med;schedule:legacy, validated when the CLI is parsed.
• Denoise complex-valued data with dwidenoise and dwidenoise2 when a phase series is available, and reject phase demodulation of magnitude-only data up front rather than failing partway through a run.
• Build the denoiser node once in init_dwi_denoising_wf, so the magnitude and complex paths differ only in what feeds the denoiser and what consumes its output.
• Connect the noise_image and bias_image outputs of the denoising workflow, which were previously unreachable.
• Generate the dwidenoise2 boilerplate from the parameters actually in effect, defaults included, following the conditional citation list the command prints in its own help. Adds 10 references to boilerplate.bib.
• Document that --dwi-denoise-window does not apply to dwidenoise2, whose patch sizes come from its schedule, and warn when a window is set with it.
• Add the nibs test dataset to CI and the test data helpers.
• Add tests covering patch2self, dwidenoise and dwidenoise2 on magnitude and complex data, plus unit tests for parameter parsing and boilerplate generation.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.33333% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.80%. Comparing base (713b370) to head (1d366ca).

Files with missing lines	Patch %	Lines
qsiprep/utils/misc.py	78.21%	12 Missing and 10 partials ⚠️
qsiprep/cli/parser.py	90.47%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1071      +/-   ##
==========================================
+ Coverage   51.62%   52.80%   +1.17%     
==========================================
  Files          71       71              
  Lines       10870    11064     +194     
  Branches     1212     1246      +34     
==========================================
+ Hits         5612     5842     +230     
+ Misses       4995     4953      -42     
- Partials      263      269       +6     

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