[gdal-dev] Optional rust library as a dependency of the Zarr driver

[Even Rouault]

Hi,

We are in the situation where we are about to have our first Rust direct 
(optional) dependency. This is for the "pcodec" lossless codec 
(https://github.com/pcodec/pcodec) that is used by some Zarr datasets. 
It offers a "cpcodec" crate with C bindings which we can use.

I've tried in https://github.com/OSGeo/gdal/pull/14779 to offer 
different options:

- by default to satisfy "casual" developers building GDAL who are mostly 
seeking ease of build and are fine with automatic download of 
dependencies (pcodec and corrosion-rs for the CMake rust integration), 
using git at CMake time,

- as well as offering more control with manual settings - either by 
pointing directly to an already installed cpcodec library, or by 
pointing to the locations of the source tree of corrosion-rs and pcodec 
- that should be more compatible of policies/constraints of packagers.

Review of people who might have integrated Rust crates in CMake C/C++ 
projects welcome. See the PR description for details.

Even

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