Currently, the `ResourceQuantity` only provides a minimal map interface with no built-in arithmetic and contains operations. This makes it unwieldy.
The intention was to avoid the ambiguities between "absent-means-zero" (guarantee like semantic) and "absent-means-infinite" (limits like semantic). Instead of only providing a minimal interface and leave the rest to the caller, we should provide two classes for each semantic:
- "ResourceQuantities" will have "absent-means-zero" semantic
- "ResourceLimits" will have "absent-means-infinite" semantic