Add `Grid::write_lz4` method

[cschwan]

To read a Grid we have the Grid::read class method, which automatically detects whether a grid was compressed. The corresponding Grid::write can't guess whether we want to write a compressed grid, of course, so we need a Grid::write_lz4 method.

[felixhekhorn]

once this is completed the python version should be stripped from

• https://github.com/N3PDF/pineko/blob/028cab55a779894cf22d38feceaa08b0b9dd0732/src/pineko/__init__.py#L33
• https://github.com/NNPDF/runcards/blob/bdc0789e00c01856e3adabbdb4aeef6bdc7f0e5d/runcardsrunner/tools.py#L55

is the decompress function actually needed https://github.com/NNPDF/runcards/blob/bdc0789e00c01856e3adabbdb4aeef6bdc7f0e5d/runcardsrunner/tools.py#L78 ? it is suspicious that it's return value is not read here: https://github.com/NNPDF/runcards/blob/bdc0789e00c01856e3adabbdb4aeef6bdc7f0e5d/runcardsrunner/external/interface.py#L39

[alecandido]

is the decompress function actually needed https://github.com/NNPDF/runcards/blob/bdc0789e00c01856e3adabbdb4aeef6bdc7f0e5d/runcardsrunner/tools.py#L78 ? it is suspicious that it's return value is not read here: https://github.com/NNPDF/runcards/blob/bdc0789e00c01856e3adabbdb4aeef6bdc7f0e5d/runcardsrunner/external/interface.py#L39

The decompress() function is actually decompressing the file whatever.lz4 -> whatever, and not loading the content in memory for later use.
In this case it is used just to reset the status of the folder to an intermediate one. and restart from there, you don't need to load the value in this place, whatever is needed, is done later on.

In any case, this is an internal issue of runcards, this is not the proper place to deal with it.

[cschwan]

Implemented in commit dfdcdcc.