feat: `qp1.quantity_from(qp2)` added #59

Job	Run time
std::format none C++23 GCC-14 Release	34s
std::format none C++23 GCC-14 Debug	58s
std::format none C++23 Clang-18 Release	52s
fmtlib none C++23 GCC-14 Release	36s
fmtlib none C++23 GCC-14 Debug	40s
fmtlib none C++23 Clang-18 Release	46s
	4m 26s

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