*.go: move the carrierd archive/tar to internal/

The feature of golang having source in a project path with "internal"
makes the code only able to be imported by the project itself.
https://docs.google.com/document/d/1e8kOo3r51b2BWtTs_1uADIA5djfXhPT36s6eHVRIvaU/edit?tab=t.0

Since we have this carried version of `archive/tar` with our byte
accounting patches, it is also means the version of archive/tar has not
kept up with upstream.

our tar-split libraries do not even utilize all the function calls of
our carried archive/tar, so might as well limit anyone else in the world
from calling them as well.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

internal/archive/tar/example_test.go

@@ -0,0 +1,72 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tar_test
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"log"
+	"os"
+
+	"github.com/vbatts/tar-split/internal/archive/tar"
+)
+
+func Example_minimal() {
+	// Create and add some files to the archive.
+	var buf bytes.Buffer
+	tw := tar.NewWriter(&buf)
+	var files = []struct {
+		Name, Body string
+	}{
+		{"readme.txt", "This archive contains some text files."},
+		{"gopher.txt", "Gopher names:\nGeorge\nGeoffrey\nGonzo"},
+		{"todo.txt", "Get animal handling license."},
+	}
+	for _, file := range files {
+		hdr := &tar.Header{
+			Name: file.Name,
+			Mode: 0600,
+			Size: int64(len(file.Body)),
+		}
+		if err := tw.WriteHeader(hdr); err != nil {
+			log.Fatal(err)
+		}
+		if _, err := tw.Write([]byte(file.Body)); err != nil {
+			log.Fatal(err)
+		}
+	}
+	if err := tw.Close(); err != nil {
+		log.Fatal(err)
+	}
+
+	// Open and iterate through the files in the archive.
+	tr := tar.NewReader(&buf)
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			break // End of archive
+		}
+		if err != nil {
+			log.Fatal(err)
+		}
+		fmt.Printf("Contents of %s:\n", hdr.Name)
+		if _, err := io.Copy(os.Stdout, tr); err != nil {
+			log.Fatal(err)
+		}
+		fmt.Println()
+	}
+
+	// Output:
+	// Contents of readme.txt:
+	// This archive contains some text files.
+	// Contents of gopher.txt:
+	// Gopher names:
+	// George
+	// Geoffrey
+	// Gonzo
+	// Contents of todo.txt:
+	// Get animal handling license.
+}