make tests more robust to new GDAL / GEOS / PROJ

[visr]

Right now when updating the minor version of the binaries, the ArchGDAL tests usually fail due to minor differences. See for instance #157.

It would be better to modify the tests to be less sensitive to these changes.

For PROJ, we already test with isapprox but probably need to introduce a larger absolute difference (@test π ≈ 3.14 atol=0.01). One millimeter differences are probably not interesting to us anyway, we just want to make sure PROJ is doing the projection.

For GEOS, the tests often rely on WKT string comparison. However the node ordering is subject to changes, as well as the geometry ordering in a GeometryCollection. Hence it is probably better to move away from WKT string comparison, and just test if the geometries are ArchGDAL.equals, like was done in https://github.com/JuliaGeo/LibGEOS.jl/pull/81.