use tuple instead of list for f-string joining because it is faster to allocate - speedup can be up to 20%

we actually know that FormattedValueNode always returns a Unicode string and no other object type => set node type accordingly

make sure f-string formatting always returns a Unicode string (even when not joining the final result in trivial cases)

fix repeated expression evaluation in f-string implementation for !s/r/a conversions by switching from macro to inline function

The cPython profiler would get confused when the wrapper and
underlying cdef function shared a name.

REL: pass license argument to setuptools.setup

Implement PEP 515: allow underscores in number literals

Remove obsolete forward about (extremely) old versions of Cython.

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