Read a transformer's regulated bus through get_regulated_bus

[m-bossart]

Remote and shared voltage control

The transformer circuit no longer carries a PSS/E bus number.
The test reads the resolved bus through get_regulated_bus and expects none on a phase-shifting circuit.

Verification

Full suite: 1660 pass, 69 broken by design, 0 errors (2026-09-24, before the PowerSystems and PowerFlowFileParser rebase).

Stack

Merge in this order.
The Julia branches pin each other's mb/remote-control branches in [sources], and each pin moves back to main or psy6 as its dependency merges.

• Step 1: Remote and shared voltage control SiennaSchemas#67: schemas
• Step 2: Regenerate for remote and shared voltage control PowerOpenAPIModels#28: Julia models
• Step 2: Regenerate the Python and TypeScript models for remote and shared voltage control power-openapi-models#14: Python and TypeScript models
• Step 2: Store remote and shared voltage control SiennaGridDB#192: database
• Step 3: Model remote and shared voltage control PowerSystems.jl#1819: types, validation and OpenAPI converters
• Step 4: Write PSS/E remote and shared voltage control to the OpenAPI document PowerFlowFileParser.jl#66: PSS/E parser
• Step 5: Read a transformer's regulated bus through get_regulated_bus #232: test fix (this PR)
• Step 6: Export and consume remote and shared voltage control PowerFlows.jl#461: PSS/E export and solver

Depends on: Sienna-Platform/PowerSystems.jl#1819, Sienna-Platform/PowerFlowFileParser.jl#66, Sienna-Platform/PowerOpenAPIModels#28.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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