test: add repo-wide option-default migration control plane

[suhaslord]

Builds the long-horizon migration framework for OpenMDAO#1251 rather than converting another isolated test file.

What this adds

• AST inventory of every get_option_defaults() call site
• per-call scope, receiver, explicit set_val keys, and dynamic-set metadata
• subsystem/domain counts to split the migration into reviewable workstreams
• machine-readable baseline under aviary/variable_info/migrations
• permanent CI ratchet: a file cannot gain calls and the repository total cannot increase
• migration guidance for lowering the baseline subsystem-by-subsystem until the utility can be deleted

Initial dependency map

• 86 calls across 25 Python files
• 230 explicit option overrides already visible around those calls
• GASP geometry: 41 calls
• aerodynamics: 17
• two-DOF mission: 13
• propulsion: 8
• solved two-DOF: 3
• energy-state mission: 2
• mass: 1
• utils: 1

This does not claim to remove all 86 uses in one review. It creates the measurable control plane that makes a multi-PR migration safe: every future slice can only drive the baseline downward.