*.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>

Author: vbatts

cmd/tar-split/tar_benchmark_test.go

@@ -7,7 +7,7 @@ import (
 
 	upTar "archive/tar"
 
-	ourTar "github.com/vbatts/tar-split/archive/tar"
+	ourTar "github.com/vbatts/tar-split/internal/archive/tar"
 )
 
 var testfile = "../../archive/tar/testdata/sparse-formats.tar"

archive/tar/common.go internal/archive/tar/common.goarchive/tar/common.go renamed to internal/archive/tar/common.go

@@ -5,12 +5,13 @@
 package tar_test
 
 import (
-	"archive/tar"
 	"bytes"
 	"fmt"
 	"io"
 	"log"
 	"os"
+
+	"github.com/vbatts/tar-split/internal/archive/tar"
 )
 
 func Example_minimal() {