Add Rust implementation of SCFG decoder

Rust port of the Ruby prototype decoder with performance
optimizations for real Hiero-style grammars:

- Rule indexing by first terminal/NT symbol for fast lookup
- Chart symbol interning (u16 IDs) instead of string hashing
- Passive chart index by (symbol, left) for direct right-endpoint lookup
- Items store rule index instead of cloned rule data

Includes CKY+ parser, chart-to-hypergraph conversion, Viterbi
decoding, derivation extraction, and JSON hypergraph I/O.

Self-filling step in parse uses grammar lookup (not just
remaining active items) to handle rules that were consumed
during the parse loop or skipped by the has_any_at optimization.

Produces identical output to the Ruby prototype on all test examples.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/rs/Cargo.toml b/rs/Cargo.toml
new file mode 100644
index 0000000..e37f06f
--- /dev/null
+++ b/rs/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "odenwald"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+clap = { version = "4", features = ["derive"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"