重构：RustCrypto 兼容接口

主要变更：
- 新增 sm2/、sm3/、sm4/ 独立 crate，实现 RustCrypto traits
  - sm2：实现 signature、elliptic-curve traits
  - sm3：实现 digest、crypto-common traits
  - sm4：实现 cipher、aead traits
- 新增 fuzz/ 模糊测试目标
- 新增 tests/sm2_proptest.rs 属性测试
- 重构 src/sm4/ 使用 RustCrypto AEAD traits
- 更新 CI 工作流支持多 crate 测试
- 更新 .gitignore 忽略 fuzz/target/

sm3/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "sm3"
+version = "0.1.0"
+edition = "2021"
+rust-version = "1.83.0"
+license = "Apache-2.0"
+description = "SM3 (ShangMi 3) hash function — GB/T 32905-2016. Pure-Rust, no_std, implements digest::Digest."
+repository = "https://github.com/kintaiW/libsmx"
+documentation = "https://docs.rs/sm3"
+categories = ["cryptography", "no-std"]
+keywords = ["crypto", "hash", "sm3", "shangmi", "digest"]
+readme = "README.md"
+
+[dependencies]
+digest = { workspace = true, features = ["block-api"] }
+
+[dev-dependencies]
+hex-literal = { workspace = true }
+digest      = { workspace = true, features = ["dev"] }
+
+[features]
+default = []
+oid     = ["digest/oid"]