Infra: Combine manual and examples build

[CalMacCQ]

Description

Quite a few changes to the repository here so I'll try to cover everything.

• Comibed manual and examples into a single sphinx build (single set of poerty dependencies and a single conf.py file. The content separation between manual and examples still exists but the build infrastructure is combined.
• notebooks are now executed and turned into html using the myst-nb library (replacing the jupyter-book library). The manual pages are still built using the jupyter_sphinx extension for now.
• I've used the Quantinuum-sphinx theme (built on top of furo) to align with the other parts of the tket docs.
• I've removed the python -> jupyter notebook conversion.
• Note that there are some visual inconsistencies between the code cells for the manual and examples. These should be fixed by moving exclusively to myst-nb for the manual and examples (I've tested this and it works). I'll do it in a follow up PR so this one doesn't get more out of hand.
• I've removed the testing of the example notebooks mentioned in the examples/ci-tested-notebooks.txt file. All of the notebooks listed in the file are executed as part of the docs build now so there is no need to test execution twice.
• note that I've combined the examples and manual under "user-guide". It may be worth setting up the following redirects to avoid link breakage.

https://tket.quantinuum.com/examples/ -> https://tket.quantinuum.com/user-guide/
https://tket.quantinuum.com/user-manual/ -> https://tket.quantinuum.com/user-guide/

I'm not sure how to do this auto-forwarding so haven't done it yet in this PR

• Finally as discussed it would be worth moving the rigetti and qiskit examples to the pytket-pyquil and pytket-qiskit repositories respectively.

CQCL/pytket-qiskit#371
CQCL/pytket-pyquil#95

Related issues

Closes #338

[CalMacCQ]

I have attempted to add some redirects for

https://tket.quantinuum.com/examples/ -> https://tket.quantinuum.com/user-guide/
https://tket.quantinuum.com/user-manual/ -> https://tket.quantinuum.com/user-guide/

in 8dd5008

Maybe the tket website repo is the best place for these? not sure