feat: use shared histogram, instead of single, general feature bump for histograms

[tlambert03]

this is a very large WIP PR that refactors the histogram widgets to have all channels on a single plot.

Screen.Recording.2026-03-29.at.10.17.17.AM.mov

We want this for QI, so the goal for now is just to make it do what we want (we'll install from this branch), and i'll delay a full review and cleanup for a few weeks from now. It has a toggle switch to retain the old behavior of having a histogram below each slider. but the default here is a single global histogram

[codecov]

Codecov Report

❌ Patch coverage is 82.67652% with 211 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.38%. Comparing base (9e52c93) to head (bff1ba3).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ndv/views/_vispy/_shared_histogram.py	82.95%	60 Missing ⚠️
src/ndv/views/_wx/_array_view.py	42.66%	43 Missing ⚠️
src/ndv/views/_pygfx/_shared_histogram.py	91.64%	37 Missing ⚠️
src/ndv/views/_qt/_array_view.py	58.18%	23 Missing ⚠️
src/ndv/views/_jupyter/_array_view.py	55.00%	18 Missing ⚠️
src/ndv/views/bases/_graphics/_histogram_utils.py	87.12%	17 Missing ⚠️
src/ndv/views/_app.py	45.45%	6 Missing ⚠️
src/ndv/controllers/_array_viewer.py	95.00%	4 Missing ⚠️
src/ndv/views/_pygfx/_util.py	50.00%	3 Missing ⚠️

❌ Your patch status has failed because the patch coverage (82.67%) is below the target coverage (85.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #267      +/-   ##
==========================================
- Coverage   85.91%   85.38%   -0.54%     
==========================================
  Files          50       53       +3     
  Lines        5980     7192    +1212     
==========================================
+ Hits         5138     6141    +1003     
- Misses        842     1051     +209     

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[tlambert03]

in the last commit, an update was made so that the histograms resample themselves based on zoom level so as to avoid drawing a huge number of (effectively invisible) bins when zoomed out, but showing integer level accuracy when zoomed in. This preserves visual accuracy without tanking performance when looking at the full range:

Screen.Recording.2026-03-31.at.9.11.50.AM.mov