Rocq-native LRAT proof checking

Integrate a Rocq-native LRAT checker, including the required Rocq code and LRAT parser adaptation, to eliminate the remaining external proof-checking component from the VFR trust boundary.

Background

The current toolchain relies on an externally developed Swansea RUP checker as part of its trusted base. A Rocq-native LRAT checker would move certificate checking entirely into the Rocq ecosystem.

The paper identifies the required implementation effort—vendoring approximately 2,000 lines of Rocq code and adapting the LRAT parser—as the remaining work for this integration.