Previously, using a Registry required a DiskCache to be passed in for
use in various methods. This was a bit cumbersome, as the DiskCache is
required for most operations, and the DefaultCache is used in most of
those cases. This change makes the DiskCache an optional field on the
Registry struct.
This also changes DefaultCache to initialize on first use. This is to
not burden clients with the cost of creating a new cache per use, or
having to hold onto a cache for the lifetime of the Registry.
Also, slip in some minor docs updates for Trace.
This commit copies (without history) the bmizerany/ollama-go repository
with the intention of integrating it into the ollama as a replacement
for the pushing, and pulling of models, and management of the cache they
are pushed and pulled from.
New homes for these packages will be determined as they are integrated
and we have a better understanding of proper package boundaries.
