cannon: Support compressed base64 pages in state.json

This compresses the pages before marshalling them. It also uses base64
instead of hex. This should reduce the memory usage of the json marshaller
and reduce the size of the files. This will support reading but not writing
hex encoded memory pages.

cannon/mipsevm/page.go

 package mipsevm
 
 import (
+	"bytes"
+	"compress/zlib"
+	"encoding/base64"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
+	"io"
+	"regexp"
 
 	"github.com/ethereum/go-ethereum/crypto"
 )
 
+func detectEncoding(data []byte) (string, error) {
+	// Regular expressions to check for base64 and hex patterns
+	base64Pattern := "^[A-Za-z0-9+/]*={0,2}$"
+	hexPattern := "^[0-9a-fA-F]*$"
+
+	if regexp.MustCompile(hexPattern).MatchString(string(data)) {
+		return "hex", nil
+	} else if regexp.MustCompile(base64Pattern).MatchString(string(data)) {
+		return "base64", nil
+	}
+	return "", fmt.Errorf("Unable to determine encoding for data: %s", data)
+}
+
 type Page [PageSize]byte
 
 func (p *Page) MarshalText() ([]byte, error) {
@@ -15,6 +34,38 @@ func (p *Page) MarshalText() ([]byte, error) {
 	return dst, nil
 }
 
+func (p *Page) MarshalJSON() ([]byte, error) {
+	var out bytes.Buffer
+	w := zlib.NewWriter(&out)
+	w.Write(p[:])
+	w.Close()
+	return json.Marshal(out.Bytes())
+}
+
+func (p *Page) UnmarshalJSON(dat []byte) error {
+	// Strip off the `"` characters at the start & end.
+	dat = dat[1 : len(dat)-1]
+	// Detect hex or bas64 encoding. legacy hex encoding is uncompressed
+	if t, err := detectEncoding(dat); err != nil {
+		return err
+	} else if t == "hex" {
+		return p.UnmarshalText(dat)
+	}
+	// Decode b64 then decompress
+	r, err := zlib.NewReader(base64.NewDecoder(base64.StdEncoding, bytes.NewReader(dat)))
+	if err != nil {
+		return err
+	}
+	defer r.Close()
+	if n, err := r.Read(p[:]); n != PageSize {
+		return fmt.Errorf("epxeted %d bytes, but got %d", PageSize, n)
+	} else if err == io.EOF {
+		return nil
+	} else {
+		return err
+	}
+}
+
 func (p *Page) UnmarshalText(dat []byte) error {
 	if len(dat) != PageSize*2 {
 		return fmt.Errorf("expected %d hex chars, but got %d", PageSize*2, len(dat))