refactor!: remove go-git backend (#39487)

Removes the go-git backend so every build uses the git CLI backend. Its
Windows performance advantage is gone, it lacks SHA-256 support, and it
breaks repositories on Windows.

The performance changes moved to
https://github.com/go-gitea/gitea/pull/39526.

Fixes https://github.com/go-gitea/gitea/issues/38359
Fixes https://github.com/go-gitea/gitea/issues/34694

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/signature.go

@@ -5,11 +5,14 @@
 package git
 
 import (
+	"fmt"
+	"io"
 	"strconv"
 	"strings"
 	"time"
 
 	"gitea.dev/modules/log"
+	"gitea.dev/modules/util"
 )
 
 // Helper to get a signature from the commit line, which looks like:
@@ -47,3 +50,25 @@ func parseSignatureFromCommitLine(line string) *Signature {
 	}
 	return sig
 }
+
+// Signature represents the Author, Committer or Tagger information.
+type Signature struct {
+	Name  string    // the committer name, it can be anything
+	Email string    // the committer email, it can be anything
+	When  time.Time // the timestamp of the signature
+}
+
+func (s *Signature) String() string {
+	return fmt.Sprintf("%s <%s>", s.Name, s.Email)
+}
+
+// Encode writes the signature for git commit object
+func (s *Signature) Encode(w io.Writer) error {
+	_, err := fmt.Fprintf(w, "%s <%s> %d %s", s.Name, s.Email, max(0, s.When.Unix()), s.When.Format("-0700"))
+	return err
+}
+
+// Decode parses the signature for git commit object
+func (s *Signature) Decode(b []byte) {
+	*s = *parseSignatureFromCommitLine(util.UnsafeBytesToString(b))
+}