[JUJU-4779] Ensure valid charm origin for local charm switches

[jack-w-shaw]

Ensure that we provide the server with a valid charm origin when switching to local charms. Previously, we simply sent back the same charm origin when switching to a local charm.

However, this is not valid, since we don't know where we switched from. If it's a charmhub charm, it's origin will not be valid.

Also, parse the revision from the new charm url the server sends us

This is equivalent to: juju/juju#16434

QA Steps

Edit line 26 of examples/local_refresh.py to point to a local ubuntu charm

$ juju deploy ubuntu
$ juju mongo
juju:PRIMARY> db.applications.find().pretty()
...
{
	"_id" : "277dae9c-abe3-4aba-83e4-0a63622e2981:ubuntu",
	"name" : "ubuntu",
	"model-uuid" : "277dae9c-abe3-4aba-83e4-0a63622e2981",
	"subordinate" : false,
	"charmurl" : "ch:amd64/focal/ubuntu-24",
	"charm-origin" : {
		"source" : "charm-hub",
		"type" : "charm",
		"id" : "DksXQKAQTZfsUmBAGanZAhpoS4dpmXel",
		"hash" : "9b2877f7ebf04b348cf40ace32fdfc6d1cc0157dea7fd6740c4ba74e0e201e5b",
		"revision" : 24,
		"channel" : {
			"risk" : "stable"
		},
		"platform" : {
			"architecture" : "amd64",
			"os" : "ubuntu",
			"channel" : "22.04"
		}
	},
	"charmmodifiedversion" : 0,
	"forcecharm" : false,
	"life" : 0,
	"unitcount" : 1,
	"relationcount" : 0,
	"minunits" : 0,
	"txn-revno" : NumberLong(3),
	"metric-credentials" : BinData(0,""),
	"exposed" : false,
	"scale" : 0,
	"passwordhash" : "",
	"provisioning-state" : null
}
 
$ python examples/local_refresh.py
$ juju mongo
juju:PRIMARY> db.applications.find().pretty()
...
{
	"_id" : "277dae9c-abe3-4aba-83e4-0a63622e2981:ubuntu",
	"name" : "ubuntu",
	"model-uuid" : "277dae9c-abe3-4aba-83e4-0a63622e2981",
	"subordinate" : false,
	"charmurl" : "local:jammy/ubuntu-13",
	"charm-origin" : {
		"source" : "local",
		"type" : "charm",
		"id" : "DksXQKAQTZfsUmBAGanZAhpoS4dpmXel",
		"hash" : "9b2877f7ebf04b348cf40ace32fdfc6d1cc0157dea7fd6740c4ba74e0e201e5b",
		"revision" : 13,
		"channel" : {
			"risk" : "stable"
		},
		"platform" : {
			"architecture" : "amd64",
			"os" : "ubuntu",
			"channel" : "22.04"
		}
	},
	"charmmodifiedversion" : 1,
	"forcecharm" : false,
	"life" : 0,
	"unitcount" : 1,
	"relationcount" : 0,
	"minunits" : 0,
	"txn-revno" : NumberLong(4),
	"metric-credentials" : BinData(0,""),
	"exposed" : false,
	"scale" : 0,
	"passwordhash" : "",
	"provisioning-state" : null
}

NOTE: This doesn't quite work as expected, but this is not a python-libjuju bug, but in juju/juju here:
https://github.com/juju/juju/blob/3.3/state/application.go#L1792-L1840

However, @hmlanigan is working on a fix (juju/juju#16315) that will resolve this, so proposing this change to python-libjuju as a stepping stone towards to complete solution

tox -e integration -- tests/integration/test_application.py::test_local_refresh

All CI tests need to pass.

[cderici]

/merge

[cderici]

/merge