Type hints (__annotations__) and coercion/categories/Cython

[mkoeppe]

The Sage coercion system guarantees the return type of certain binary operations. This should be made known to typing - for introspection purposes in IDEs and for static checkers.

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References:

• PEP 563 -- Postponed Evaluation of Annotations - upcoming change in Python 3.10

• https://cython.readthedocs.io/en/latest/src/tutorial/pure.html?highlight=annotations#static-typing

CC: @tobiasdiez @mwageringel @egourgoulhon @tscrim @nthiery

Component: coercion

Issue created by migration from https://trac.sagemath.org/ticket/30511

[mkoeppe]

comment:1

Setting new milestone based on a cursory review of ticket status, priority, and last modification date.