# Objective
- Part of #20115
We want to encapsulate each part of `ScheduleGraph` into its own
specific struct to make parts of it easier to reuse and maintain.
## Solution
- Pulled `ScheduleGraph::systems` and `ScheduleGraph::system_conditions`
into a `Systems` struct and added a field for this new struct to
`ScheduleGraph`
- Broke up `ScheduleGraph::uninit` into `Systems::uninit` and
`SystemSets::uninit` to eliminate `ScheduleGraph`'s direct field access
of these types
- Removed node and condition accessors from `ScheduleGraph`; the same
operations are now available on `Systems` and `SystemSets` instead
(accessible via their `pub` fields on `ScheduleGraph`)
- Moved `Systems`, `SystemSets`, `SystemNode`, `SystemWithAccess`, and
`ConditionWithAccess` into a separate file.
## Testing
Added two new tests covering the API surface of `Systems` and
`SystemSets`, respectively.
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Co-authored-by: Chris Russell <8494645+chescock@users.noreply.github.com>
