`Measure` should subclass `Real` itself

[yunruse]

A Measure cannot be turned into a Fraction easily:

>>> a = (lunation % day) / day
>>> a
0.53058912
>>> Fraction(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/fractions.py", line 140, in __new__
    raise TypeError("argument should be a string "
TypeError: argument should be a string or a Rational instance

We can see already that Measure is a Generic[T] where T is a Real. This could be extended; Measure should subclass the Real itself rather than holding it as its value.

This would vastly improve interoperability and also reduce the necessary methods added to keep Real compatibility (.imag, __int__ and so on).

Indeed it may be possible to later support the superclass Complex, though the methods dropped by this may cause some typing headaches.