feat: vendor bodgit/sevenzip package to remove go4.org dependency

Vendored the sevenzip package to eliminate dependency chain:
- sevenzip -> go4.org -> 25+ Google/Cloud/telemetry packages

Changes:
- Added internal/sevenzip/ with full package source
- Inlined go4.org/readerutil into multireaderat.go
- Updated all internal imports to use bookhoard/internal/sevenzip
- Preserved .cb7 comic archive support

This reduces bloat by ~4.9 MB and removes unused telemetry
dependencies while maintaining all functionality.

internal/sevenzip/internal/brotli/reader.go

@@ -0,0 +1,113 @@
+// Package brotli implements the Brotli decompressor.
+package brotli
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"sync"
+
+	"github.com/andybalholm/brotli"
+	"github.com/bodgit/plumbing"
+)
+
+type readCloser struct {
+	c io.Closer
+	r *brotli.Reader
+}
+
+const (
+	frameMagic  uint32 = 0x184d2a50
+	frameSize   uint32 = 8
+	brotliMagic uint16 = 0x5242 // 'B', 'R'
+)
+
+var (
+	//nolint:gochecknoglobals
+	brotliReaderPool sync.Pool
+
+	errAlreadyClosed = errors.New("brotli: already closed")
+	errNeedOneReader = errors.New("brotli: need exactly one reader")
+)
+
+// This isn't part of the Brotli format but is prepended by the 7-zip implementation.
+type headerFrame struct {
+	FrameMagic       uint32
+	FrameSize        uint32
+	CompressedSize   uint32
+	BrotliMagic      uint16
+	UncompressedSize uint16 // * 64 KB
+}
+
+func (rc *readCloser) Close() error {
+	if rc.c == nil || rc.r == nil {
+		return errAlreadyClosed
+	}
+
+	if err := rc.c.Close(); err != nil {
+		return fmt.Errorf("brotli: error closing: %w", err)
+	}
+
+	brotliReaderPool.Put(rc.r)
+	rc.c, rc.r = nil, nil
+
+	return nil
+}
+
+func (rc *readCloser) Read(p []byte) (int, error) {
+	if rc.r == nil {
+		return 0, errAlreadyClosed
+	}
+
+	n, err := rc.r.Read(p)
+	if err != nil && !errors.Is(err, io.EOF) {
+		err = fmt.Errorf("brotli: error reading: %w", err)
+	}
+
+	return n, err
+}
+
+// NewReader returns a new Brotli io.ReadCloser.
+func NewReader(_ []byte, _ uint64, readers []io.ReadCloser) (io.ReadCloser, error) {
+	if len(readers) != 1 {
+		return nil, errNeedOneReader
+	}
+
+	hr, b := new(headerFrame), new(bytes.Buffer)
+	b.Grow(binary.Size(hr))
+
+	// The 7-Zip Brotli compressor adds a 16 byte frame to the beginning of
+	// the data which will confuse a pure Brotli implementation. Read it
+	// but keep a copy so we can add it back if it doesn't look right
+	if err := binary.Read(io.TeeReader(readers[0], b), binary.LittleEndian, hr); err != nil {
+		if !errors.Is(err, io.EOF) {
+			err = fmt.Errorf("brotli: error reading frame: %w", err)
+		}
+
+		return nil, err
+	}
+
+	var reader io.ReadCloser
+
+	// If the header looks right, continue reading from that point
+	// onwards, otherwise prepend it again and hope for the best
+	if hr.FrameMagic == frameMagic && hr.FrameSize == frameSize && hr.BrotliMagic == brotliMagic {
+		reader = readers[0]
+	} else {
+		reader = plumbing.MultiReadCloser(io.NopCloser(b), readers[0])
+	}
+
+	r, ok := brotliReaderPool.Get().(*brotli.Reader)
+	if ok {
+		_ = r.Reset(reader)
+	} else {
+		r = brotli.NewReader(reader)
+	}
+
+	return &readCloser{
+		c: readers[0],
+		r: r,
+	}, nil
+}