feat: 添加 README，更新 .gitignore，移除 JE-Skin/eskin-finger-sdk

- 添加 README.md 项目文档
- 更新 .gitignore 排除 JE-Skin/、eskin-finger-sdk/ 及构建产物
- 从 git 跟踪中移除 JE-Skin 和 eskin-finger-sdk

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/serial_core/utils.rs

@@ -7,4 +7,4 @@ pub fn calc_crc8_itu(c: &[u8]) -> u8 {
 
 pub fn elapsed_millis(start_at: Instant) -> u64 {
     start_at.elapsed().as_millis() as u64
-}
+}