Add `RealNumber` #799

Job	Run time
Mypy	23s
Typos	4s
Documentation	49s
Tests for downstream project loopy	3m 51s
Pylint	55s
Tests for downstream project pytential	54m 17s
Pytest on Py3.10	39s
Tests for downstream project pytato	6m 16s
Ruff	7s
Pytest on Py3.12	36s
Pytest on Py3.x	34s
	1h 8m 31s

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