add support for injecting checksums for cargo crates

[Flamefire]

Even though the crates are recognized as sources for Cargo easyconfigs the checksums are not written, at least when neither 'source_urls', 'sources' nor 'patches' are present.

Handle crates like sources and add test.

[boegel]

Hmm, this approach is a bit weird, as it breaks the boundary between framework and easyblocks, since crates is not a general easyconfig parameter...

Thoughts on this @Micket?

[boegel]

Maybe we come up with an approach that would also work for components (in Bundle easyblock)?

[Flamefire]

As discussed in the confcall I added a method src_parameter_names to the easyblock class.

In the Cargo easyblock we can override this to also return "crates".

For components I don't think this is useful. For now they look like:

components = [
    (name, version, {
        'source_urls': ['https://poppler.freedesktop.org/'],
        'sources': [SOURCE_TAR_XZ],
        'checksums': ['86b09e5a02de40081a3916ef8711c5128eaf4b1fc59d5f87d0ec66f04f595db4'],
        'configopts': "-DENABLE_BOOST=ON",
    }),
    ('poppler-data', '0.4.10', {
        'source_urls': ['https://poppler.freedesktop.org/'],
        'sources': [SOURCE_TAR_GZ],
        'checksums': ['6e2fcef66ec8c44625f94292ccf8af9f1d918b410d5aa69c274ce67387967b30'],
    }),
]

While the Bundle easyblock seemingly supports specifying checksums for everything at the top-level (outside the components) I don't think it actually does: It creates a full list of sources, patches and checksums during __init__ but the actual checksum check (at least the contrib check) requires them in each component as above.

However with this design it would be possible to add the checksum list after the components but then we'd need to include logic to remove them from each component

The general approach is different here anyway: crates are just another way to specify sources while components are similar to exts_list which yield actual easyblock instances.