chore(ci/lint/config): update golangci-lint configuration and workflows

Refactor the golangci-lint configuration to use the latest version and
update GitHub Actions workflows. Key changes include:

- Update golangci-lint to v2.6
- Update GitHub Actions to use latest checkout and setup-go actions
- Update Go versions in test matrix
- Remove deprecated cache steps
- Update Makefile golangci-lint tool version
- Minor documentation formatting improvements

validate.go

@@ -1,13 +1,13 @@
 // Package validate is yet another Go struct/object validation package, with a
 // focus on simplicity, flexibility, and full control over validation logic.
 //
-// Interface
+// # Interface
 //
 // To add validation to any type, simply implement the Validatable interface:
 //
-//  type Validatable interface {
-//      Validate() error
-//  }
+//	type Validatable interface {
+//		Validate() error
+//	}
 //
 // To mark a object as failing validation, the Validate method simply needs to
 // return a error.
@@ -17,7 +17,7 @@
 // can be fully validated, and the nested path to each object is tracked and
 // reported back any validation errors.
 //
-// Multiple Errors
+// # Multiple Errors
 //
 // Multiple errors can be reported from the Validate method using one of the
 // available Append helper functions which append errors together. Under the
@@ -25,53 +25,53 @@
 // a single error return type, and you can in fact just directly use multierr in
 // the a type's Validate method.
 //
-// Structs and Field-specific Errors
+// # Structs and Field-specific Errors
 //
 // When validating a struct, you are likely to have multiple errors for multiple
 // fields. To specify which field on the struct the error relates to, you have
 // to return a *validate.Error instead of a normal Go error type. For example:
 //
-//  type Book struct {
-//      Title  string
-//      Author string
-//  }
+//	type Book struct {
+//		Title  string
+//		Author string
+//	}
 //
-//  func (s *Book) Validate() error {
-//      var errs error
+//	func (s *Book) Validate() error {
+//		var errs error
 //
-//      if s.Title == "" {
-//          errs = validate.Append(errs, &validate.Error{
-//              Field: "Title", Msg: "is required",
-//          })
-//      }
+//		if s.Title == "" {
+//			errs = validate.Append(errs, &validate.Error{
+//				Field: "Title", Msg: "is required",
+//			})
+//		}
 //
-//      if s.Author == "" {
-//          // Yields the same result as the Title field check above.
-//          errs = validate.AppendFieldError(errs, "Author", "is required")
-//      }
+//		if s.Author == "" {
+//			// Yields the same result as the Title field check above.
+//			errs = validate.AppendFieldError(errs, "Author", "is required")
+//		}
 //
-//      return errs
-//  }
+//		return errs
+//	}
 //
 // With the above example, if you validate a empty *Book:
 //
-//  err := validate.Validate(&Book{})
-//  for _, e := range validate.Errors(err) {
-//      fmt.Println(e.Error())
-//  }
+//	err := validate.Validate(&Book{})
+//	for _, e := range validate.Errors(err) {
+//		fmt.Println(e.Error())
+//	}
 //
 // The following errors would be printed:
 //
-//  Title: is required
-//  Kind: is required
+//	Title: is required
+//	Kind: is required
 //
-// Error type
+// # Error type
 //
 // All errors will be wrapped in a *Error before being returned, which is used
 // to keep track of the path and field the error relates to. There are various
 // helpers available to create Error instances.
 //
-// Handling Validation Errors
+// # Handling Validation Errors
 //
 // As mentioned above, multiple errors are wrapped up into a single error return
 // value using go.uber.org/multierr. You can access all errors individually with
@@ -79,7 +79,7 @@
 // function is just wrapper around multierr.Errors(), so you could use that
 // instead if you prefer.
 //
-// Struct Field Tags
+// # Struct Field Tags
 //
 // Fields on a struct which customize the name via a json, yaml, or form field
 // tag, will automatically have the field name converted to the name in the tag
@@ -88,7 +88,7 @@
 // You can customize the field name conversion logic by creating a custom
 // Validator instance, and calling FieldNameFunc() on it.
 //
-// Nested Validatable Objects
+// # Nested Validatable Objects
 //
 // All items/fields on any structs, maps, slices or arrays which are encountered
 // will be validated if they implement the Validatable interface. While
@@ -103,30 +103,30 @@
 // As an example, if our Book struct from above is nested within the following
 // structs:
 //
-//  type Order struct {
-//      Items []*Item `json:"items"`
-//  }
+//	type Order struct {
+//		Items []*Item `json:"items"`
+//	}
 //
-//  type Item struct {
-//      Book *Book `json:"book"`
-//  }
+//	type Item struct {
+//		Book *Book `json:"book"`
+//	}
 //
 // And we have a Order where the book in the second Item has a empty Author
 // field:
 //
-//  err := validate.Validate(&Order{
-//      Items: []*Item{
-//          {Book: &Book{Title: "The Traveler", Author: "John Twelve Hawks"}},
-//          {Book: &Book{Title: "The Firm"}},
-//      },
-//  })
-//  for _, e := range validate.Errors(err) {
-//      fmt.Println(e.Error())
-//  }
+//	err := validate.Validate(&Order{
+//		Items: []*Item{
+//			{Book: &Book{Title: "The Traveler", Author: "John Twelve Hawks"}},
+//			{Book: &Book{Title: "The Firm"}},
+//		},
+//	})
+//	for _, e := range validate.Errors(err) {
+//		fmt.Println(e.Error())
+//	}
 //
 // Then we would get the following error:
 //
-//  items.1.book.Author: is required
+//	items.1.book.Author: is required
 //
 // Note how both "items" and "book" are lower cased thanks to the json tags on
 // the struct fields, while our Book struct does not have a json tag for the