Have CI action for notebook tests divide work across runners

[rileyjmurray]

CI tests for jupyter notebooks are only run with the beta-master action, and only one runner within that action (ubuntu-latest, python 3.13, cython). These tests take 45 minutes on their own, to say nothing about the ~10 minutes of unit tests before we get to notebook tests.

At the very least we should have a runner within this action that immediately builds pyGSTi and runs these tests -- no waiting for unittests to pass. We could also consider creating infrastructure to have multiple runners which handle different notebook tests in an embarassingly parallel way.

The beta-master action takes about 19 minutes (at time of filing this issue) if not for these notebook tests. So the natural goal would be to split up notebook work so the whole thing takes about 20 minutes.

[rileyjmurray]

We'll need to profile notebook tests on CI runners first. Worth profiling locally as well.

[rileyjmurray]

Durations from CI!

============================= slowest 25 durations =============================
802.20s call     docs/markdown/examples/Leakage-automagic.ipynb::Cell 2
672.44s call     docs/markdown/examples/Robust-GST.ipynb::Cell 2
417.02s call     docs/markdown/objects/Instruments.ipynb::Cell 12
152.54s call     docs/markdown/examples/QutritGST.ipynb::Cell 7
113.42s call     docs/markdown/utilities/ModelTesting-functions.ipynb::Cell 7
95.12s call     docs/markdown/examples/QutritGST.ipynb::Cell 8
86.86s call     docs/markdown/gst/Driverfunctions.ipynb::Cell 8
85.05s call     docs/markdown/protocols/ParityBenchmarking.ipynb::Cell 19
84.95s call     docs/markdown/rb/MultiRBExperiments.ipynb::Cell 3
78.38s call     docs/markdown/overview/00-Protocols.ipynb::Cell 1
76.74s call     docs/markdown/reporting/ReportGeneration.ipynb::Cell 8
73.94s call     docs/markdown/gst/Driverfunctions.ipynb::Cell 6
61.91s call     docs/markdown/protocols/ParityBenchmarking.ipynb::Cell 20
61.70s call     docs/markdown/examples/Robust-GST.ipynb::Cell 3
61.49s call     docs/markdown/protocols/ParityBenchmarking.ipynb::Cell 22
59.65s call     docs/markdown/gst/Protocols.ipynb::Cell 13
56.98s call     docs/markdown/rb/Overview.ipynb::Cell 2
56.78s call     docs/markdown/protocols/ParityBenchmarking.ipynb::Cell 21
56.58s call     docs/markdown/gst/Driverfunctions.ipynb::Cell 10
50.99s call     docs/markdown/rb/MirrorRB-Universal-Gate-Sets.ipynb::Cell 4
50.62s call     docs/markdown/gst/Protocols.ipynb::Cell 11
49.61s call     docs/markdown/gst/Protocols.ipynb::Cell 22
46.97s call     docs/markdown/gst/Protocols.ipynb::Cell 15
45.78s call     docs/markdown/rb/CliffordRB.ipynb::Cell 9
43.83s call     docs/markdown/examples/ProceduralErrorBars.ipynb::Cell 1
================ 1056 passed, 48 skipped in 2701.13s (0:45:01) =================