Current sensor: statistics + observability

[mgovers]

Part of #547

This implements:

• In the observability check, treat the current sensor the same as power sensor. They both contribute to observability.
• In the measured values, treat the current sensor similarly as power sensor, but accumulate separately.
  • If there is no voltage angle measurement but there are global angle current sensors in the connected component of the grid, throw an error
  • If there is a mixture of local and global angle current sensors on the same terminal (i.e., the same branch_from or branch_to of the same component), throw an error.
    • NOTE: it is supported to have a mixture as long as they are on different terminals, e.g., a local angle current sensor on the branch from side and a global angle current sensor on the branch to side of the same branch is OK.
• Fixes prepare state estimation for current sensor
• Refactors some measured values logic that is more generic

[figueroa1395]

Mostly nitpicks from my side. Looks good overall.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
94.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[figueroa1395]

No further comments. Looks good to me.