Method to fetch an Artifact.
Note that this method tries all the coursier.CachePolicyies of this cache straightaway. During resolutions, you should
prefer to try all repositories for the first policy, then the other policies if needed (in pseudo-code,
for (policy <- policies; repo <- repositories) …, rather than
for (repo <- repositories, policy <- policies) …). You should use the fetchs method in that case.
for (policy <- policies; repo <- repositories) …
for (repo <- repositories, policy <- policies) …
Sequence of Repository.Fetch able to fetch an Artifact.
Each element correspond to a coursier.CachePolicy of this Cache. You may want to pass each of them to
a non empty sequence
This method computes the task needed to get a file.