修复 no_std 测试并升级 MSRV 至 1.83.0

- 修复 cargo test --no-default-features --lib 编译错误
  - SM3 测试：移除 alloc 依赖，改用手动十六进制解析
  - SM4 modes 测试：添加 #[cfg(feature = "alloc")]
- MSRV 升级至 1.83.0（crypto-bigint 0.6.x 的 ConstMontyForm 所需）
- 更新 CI 工作流中的 MSRV 版本
- 修正 Cargo.toml 仓库链接

Cargo.toml

@@ -2,12 +2,12 @@
 name = "libsmx"
 version = "0.1.0"
 edition = "2021"
-rust-version = "1.72.0"
+rust-version = "1.83.0"
 license = "Apache-2.0"
 description = "Pure-Rust, no_std, constant-time SM2/SM3/SM4/SM9 Chinese cryptography (GB/T 32918/32905/32907/38635)"
-repository = "https://github.com/aspect-building/libsmx"
+repository = "https://github.com/kintaiW/libsmx"
 documentation = "https://docs.rs/libsmx"
-homepage = "https://github.com/aspect-building/libsmx"
+homepage = "https://github.com/kintaiW/libsmx"
 categories = ["cryptography", "no-std"]
 keywords = ["sm2", "sm3", "sm4", "sm9", "gmssl"]
 readme = "README.md"