Description of change
This patch contains preparatory work for added branch-based charm configuration to the model cache. In particular: - Each model now has its own pub/sub hub for better scalability. - Pub/sub topics previously needing a model UUID name-space no longer do. - The cache now returns deep-copied units instead of references, as per branches. - For units and branches now returning copies, the unneeded lock infrastructure is removed. - Some events previously specific to LXD profile watching are now generic.
QA steps
Same as for https://github.com/juju/juju/pull/10062
Documentation changes
None.
Bug reference
N/A.
该提问来源于开源项目：juju/juju
