More tests for complexobject.c

[skirpichev]

Right now ./python -m test test_complex test_cmath only partially cover implementation of the complex object. Some code/branches are just inaccessible (e.g. L135-136 or mask <= 0 on L166; line numbers are wrt to 54fbfa8). There are only indirect tests for C-API functions (e.g. PyComplex_RealAsDouble, PyComplex_ImagAsDouble).

Linked PRs

• gh-109802: removed inaccessible code from complexobject.c #109642
• gh-109802: Increase test coverage for complexobject.c #112452
• [3.12] gh-109802: Increase test coverage for complexobject.c (GH-112452) #112489
• gh-109802: Add coverage test for complex_abs() #117449