Regenerate C Headers

Goal

Keep the checked-in copies of the plugin ABI header synchronized with the Rust source they are generated from.

Scope

Only ovstorage_plugin.h is generated, from the ovstorage-plugin crate. It has to be: plugins are prebuilt cdylibs loaded at runtime, so host and plugin compile separately and must agree on struct layout.

ovstorage.h is NOT generated. The C application API ships as source, so consumers compile that header together with the implementation it declares and there is no binary boundary to freeze. Edit it directly, alongside ovstorage-c-source/src; the link-completeness gate in make c-source-examples is what holds the two in agreement.