Port the no-delimiter external-sequence block scanner, match splitting, repcode updates, validation, and sequence/literal storage behind a narrow C shim. Preserve trailing bytes as literals when the sequence buffer ends before the requested block, and remove the obsolete C validation wrapper.
Test Plan:
- cargo test --manifest-path rust/Cargo.toml --no-default-features --features compression (242 passed)
- cargo clippy --manifest-path rust/Cargo.toml --no-default-features --features compression [--benches|--tests] (clean)
- cargo +nightly fmt --manifest-path rust/Cargo.toml (clean)
- make -B -C lib -j2 lib (passed)
- make -C tests -j2 test-zstream (84 deterministic; 5960 and 8307 randomized passed)
- make -C tests -j2 test-fuzzer (existing test 56 CCtx-reuse mismatch; also fails at 37eb75758)
- make -C tests -j2 test-zstd (existing Rust CLI --patch-from gap)