Replace OpenInterval, RealLine instances by instances of a subclass of DifferentiableManifold+RealSet

[mkoeppe]

(from discussion in #30832 comment:14)

We represent open intervals and the real line, when they are to be considered as manifold objects, as an instance of a subclass of DifferentiableManifold and RealSet.

Likewise, arbitrary finite unions of intervals become instances of a subclass of ManifoldSubset and RealSet.

Compared to ManifoldSubset, the methods union and intersection are replaced by a more specific implementation.

OpenInterval and RealLine will no longer be classes, only constructors.

More general implementation using #31688 (pullbacks of subsets under continuous maps). In this case we would not need to subclass RealSet, but rather we would use a pullback.

This will also solve #30830 comment:18:

OpenInterval should silently return a RealLine instance if lower == minus_infinity and upper == infinity.

Some API changes to consider:

• constructor RealSets.point clashes with Manifold.point, could replace by RealSets.singleton.
• deprecate OpenInterval.upper_bound, OpenInterval.lower_bound
• RealSet: Replace is_included_in, is_disjoint_from by is_subset, is_disjoint #31927: RealSet: Replace is_included_in, is_disjoint_from by is_subset, is_disjoint
• RealSet.are_pairwise_disjoint, contains
• ManifoldSubset.complement has optional arg superset
• RealSet.open vs OpenInterval.open_interval
• RealSet.cardinality, n_components
• ManifoldSubset.has_defined_points

Depends on #31881

CC: @egourgoulhon @tscrim @mjungmath

Component: manifolds

Issue created by migration from https://trac.sagemath.org/ticket/31878

[mkoeppe]

Dependencies: #30832, #31880, #31877

[mkoeppe]

Changed dependencies from #30832, #31880, #31877 to #30832, #31880, #31877, #31688

[mkoeppe]

Changed dependencies from #30832, #31880, #31877, #31688 to #31881