Observability: re-configure relevant test cases for full observability check

[Jerry-Jinfeng-Guo]

This PR fixes/reconfigures unit/validation test cases for #1136

• ill_conditioned_system/leaf-without-power-sensor-meshed from a0140b7 was faulty
• re-configure validation cases from Full observability check: meshed validation cases #1044 to remove the fake pass

In the unit test for observability, existing tests are essentially validation tests. There is no presence of real unit test per se. The addition of unit test there is therefore out of the scope.

[Copilot]

Pull Request Overview

This PR reconfigures test cases for state estimation observability to reflect the implementation of full observability checks for meshed grids. It removes workarounds and expected failures that were in place before the observability feature was fully implemented.

• Removes xpass configuration that was marking a test as unexpectedly passing
• Fixes the leaf-without-power-sensor-meshed test case by updating expected output data
• Removes xfail configuration that was expecting failures due to unimplemented features

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tests/data/state_estimation/meshed-network-observability/02-unobservable-with-branch-measurement/params.json	Removes xpass configuration now that observability check is implemented
tests/data/state_estimation/ill-conditioned-system/leaf-without-power-sensor-meshed/sym_output.json	Updates expected output with corrected node data and removes sensor residual fields
tests/data/state_estimation/ill-conditioned-system/leaf-without-power-sensor-meshed/params.json	Removes xfail configuration as the bug has been resolved

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud

[figueroa1395]

Should we wait until #1136 is merged before merging this one? Good to go in my eyes besides the CI checks (unrelated to this PR itself).