docs: add xerror package doc

docs/xerror.md

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+# Xerror
+Package xerror implements helpers for errors.
+
+<div STYLE="page-break-after: always;"></div>
+
+## Source:
+
+- [https://github.com/duke-git/lancet/blob/main/xerror/xerror.go](https://github.com/duke-git/lancet/blob/main/xerror/xerror.go)
+
+<div STYLE="page-break-after: always;"></div>
+
+## Usage:
+```go
+import (
+    "github.com/duke-git/lancet/xerror"
+)
+```
+
+<div STYLE="page-break-after: always;"></div>
+
+## Index
+- [Unwrap](#Unwrap)
+
+<div STYLE="page-break-after: always;"></div>
+
+## Documentation
+
+
+
+### <span id="Unwrap">Unwrap</span>
+<p>Unwrap if err is nil then it returns a valid value. If err is not nil, Unwrap panics with err.</p>
+
+<b>Signature:</b>
+
+```go
+func Unwrap[T any](val T, err error) T
+```
+<b>Example:</b>
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/duke-git/lancet/xerror"
+)
+
+func main() {
+    _, err := strconv.Atoi("4o2")
+	defer func() {
+		v := recover()
+		fmt.Println(err.Error()) // err.Error() == v.(*strconv.NumError).Error()
+	}()
+
+	xerror.Unwrap(strconv.Atoi("4o2"))
+}
+```

docs/xerror_zh-CN.md

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+# Xerror
+xerror错误处理逻辑封装
+
+<div STYLE="page-break-after: always;"></div>
+
+## 源码:
+
+- [https://github.com/duke-git/lancet/blob/main/xerror/xerror.go](https://github.com/duke-git/lancet/blob/main/xerror/xerror.go)
+
+<div STYLE="page-break-after: always;"></div>
+
+## 用法:
+```go
+import (
+    "github.com/duke-git/lancet/xerror"
+)
+```
+
+<div STYLE="page-break-after: always;"></div>
+
+## 目录
+- [Unwrap](#Unwrap)
+
+<div STYLE="page-break-after: always;"></div>
+
+## 文档
+
+
+
+### <span id="Unwrap">Unwrap</span>
+<p>如果err为nil则展开，则它返回一个有效值。 如果err不是nil则Unwrap使用err发生恐慌。</p>
+
+<b>函数签名:</b>
+
+```go
+func Unwrap[T any](val T, err error) T
+```
+<b>例子:</b>
+
+```go
+package main
+
+import (
+    "fmt"
+    "github.com/duke-git/lancet/xerror"
+)
+
+func main() {
+    _, err := strconv.Atoi("4o2")
+	defer func() {
+		v := recover()
+		fmt.Println(err.Error()) // err.Error() == v.(*strconv.NumError).Error()
+	}()
+
+	xerror.Unwrap(strconv.Atoi("4o2"))
+}
+```