Implement infinite Git HTTP server

This server generates a new commit every time someone pulls from it.
Features:
- Pure Go implementation of Git object format and protocols
- No dependency on git CLI commands
- Thread-safe commit generation
- Read-only Git HTTP smart protocol support
- Comprehensive test suite

Each pull creates a new commit with a unique file containing a timestamp
and counter, making the repository grow infinitely with each pull operation.

Co-Authored-By: Claude <noreply@anthropic.com>

internal/object/commit.go

@@ -0,0 +1,75 @@
+package object
+
+import (
+	"bytes"
+	"fmt"
+	"time"
+)
+
+// Commit represents a Git commit object.
+type Commit struct {
+	Tree       string    // SHA-1 hash of the tree object
+	Parent     string    // SHA-1 hash of the parent commit (empty for initial commit)
+	Author     string    // Author name and email
+	AuthorDate time.Time // Author timestamp
+	Committer  string    // Committer name and email
+	CommitDate time.Time // Commit timestamp
+	Message    string    // Commit message
+}
+
+// NewCommit creates a new commit object.
+func NewCommit(tree, parent, author, committer, message string) *Commit {
+	now := time.Now()
+	return &Commit{
+		Tree:       tree,
+		Parent:     parent,
+		Author:     author,
+		AuthorDate: now,
+		Committer:  committer,
+		CommitDate: now,
+		Message:    message,
+	}
+}
+
+// Type returns the object type.
+func (c *Commit) Type() Type {
+	return TypeCommit
+}
+
+// Serialize returns the commit content in Git format.
+func (c *Commit) Serialize() []byte {
+	var buf bytes.Buffer
+
+	// Tree reference
+	fmt.Fprintf(&buf, "tree %s\n", c.Tree)
+
+	// Parent reference (if exists)
+	if c.Parent != "" {
+		fmt.Fprintf(&buf, "parent %s\n", c.Parent)
+	}
+
+	// Author
+	fmt.Fprintf(&buf, "author %s %d %s\n",
+		c.Author,
+		c.AuthorDate.Unix(),
+		c.AuthorDate.Format("-0700"))
+
+	// Committer
+	fmt.Fprintf(&buf, "committer %s %d %s\n",
+		c.Committer,
+		c.CommitDate.Unix(),
+		c.CommitDate.Format("-0700"))
+
+	// Empty line before message
+	buf.WriteByte('\n')
+
+	// Commit message
+	buf.WriteString(c.Message)
+
+	// Ensure message ends with newline
+	if len(c.Message) > 0 && c.Message[len(c.Message)-1] != '\n' {
+		buf.WriteByte('\n')
+	}
+
+	return buf.Bytes()
+}