This PR adds a DependencySnapshot type. This type can be created from anything that implements DependencyProvider. The snapshot can be serialized and later be used as a DependencyProvider. This allows capturing ecosystem-specific implementations in a single file format which makes it great for running extensive benchmarks for different ecosystems.

Creating a snapshot requires an ecosystem implementation. An example can be found in conda/rattler#741.

I also included a little tool called solve-snapshot that will solve for all package names found in a single snapshot and output timing information.