Meson: make pari a dependency of cypari2

[tobiasdiez]

Small improvement: We never use PARI directly (and we shouldn’t); we only use cypari2. However, PARI must still be declared as a dependency because cypari2 links against it and requires it at runtime. To make this explicit in the Meson build, we declare PARI as a dependency of cypari2, not of our own code. (I also asked on the cython mailing list if there is a clearer way to avoid the explicit pari dependency).

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[dimpase]

we have spkgs eclib, lcalc, and sympow which do use pari without cypari. So I don't quite understand the claim