Replace the SimilaritySurface hierarchy with categories

[saraedum]

Fixes #132 and hopefully gets rid of all of the boilerplate that is currently necessary to expose functionality in both surface hierarchies.

Checklist

• Added an entry in doc/news/.
• Added a test for this change.
• Added new .py files to the documentation in doc/geometry or doc/graphical.

Dependencies

• Do not use assertions for control flow #219
• Drop unused/outdated code from surface_objects #221
• Fix pickling of surfaces #223
• exact reals do not know when they might be algebraic exact-real#172
• exact-reals do not know when they are squares exact-real#173

TODO

• We cannot compute the stratum of some half-translation surfaces. See https://sagemath.zulipchat.com/#narrow/stream/271193-polygon/topic/category/near/355786162.2E01. This now shows as an error when printing these surfaces. (postponed as Cannot compute stratum of some translation surfaces #227)
• __eq__ should be a very strict notion of equality always (same type & indistinguishable); make sure this is always the case and documented
• labels() does not work for non-connected surfaces; this is not a new problem. There is only a single base label so how should we iterate non-connected surfaces?
• Make sure that all the example constructions still work (except for the ones defining infinite surfaces.)
• Make sure that there are no new #TODO markers in the code anymore.
• Speed up doctests (we are now doctesting much more through categories, and tests take about 55 seconds on my machine which is annoying.)
• Document what's at the bottom of surface.py.

Fix Speed Regressions

Generically, some tests deteriorated:

• similarity_surface.py + rational_similarity_surface.py 3s → 11.2s → 5.6s → 3s
• delaunay.py 2.16s → 15.03s → 4s
• fundamental_group.py 0.29s → 0.97s → 0.19s
• mappings.py 0.37s → 0.82s → 0.4s

There are specific problems with performance:

• is_rational_surface() (which is new) is very slow. (but it's not called automatically anymore.)
• printing of surfaces is sometimes very slow

[github-actions]

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