QA: migrate to SciMLTesting 2.4

[ChrisRackauckas-Claude]

Summary

• Migrate all BoundaryValueDiffEq packages and QA environments to SciMLTesting 2.4.
• Replace dynamic reexport discovery with fixed audited reexport inventories, while retaining strict owned-API documentation checks.
• Document developer extension interfaces and ODEInterface algorithms at their definitions.

Validation

• Strict SciMLTesting 2.4 QA: root and all six component packages on Julia 1.10.
• Strict root QA on Julia 1.12.
• BoundaryValueDiffEqCore package tests.
• Scoped Runic check with docstrings.

Ignore until reviewed by @ChrisRackauckas.