Note

Medium Risk
Introduces new FFI surface area and tweaks GC scanning/callback plumbing in numeric_range_tree, where mistakes can lead to UB, leaks, or subtle GC/cardinality regressions; changes are largely additive but touch unsafe boundaries.

Overview
Adds a new numeric_range_tree_ffi crate that exposes the Rust numeric_range_tree to C via a generated headers/numeric_range_tree.h, including lifecycle (NewNumericRangeTree/_Free), insert (NumericRangeTree_Add), query (NumericRangeTree_Find), iteration, range accessors, and FT.DEBUG-oriented dump/summary helpers.

Refactors numeric-range-tree internals to better support GC/FFI: NumericIndex::scan_gc now accepts an optional per-entry repair callback, NumericRangeNode::scan_gc is added to compute both GC deltas and HLL cardinality registers, and several result structs are marked #[repr(C)] with new raw-part constructors (Key/NodeIndex) for round-tripping through C. Build/bindgen is updated to blocklist numeric_range_tree.h, inverted_index_ffi exposes fork_gc publicly, and workspace lock/hack dependencies are updated (notably adding redis-module).

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