lisk-codec decode does not guarantee `encode(decode(val)) == val`

[shuse2]

Expected behavior

With any value which can be successfully decoded, encode(decode(val)) == val should be true.

Actual behavior

• wire-type is not checked, so with wrong wire type it will be still decodable
• varint can be represented in longer form and still decoded correctly
• There are some string which cannot be decode/encode to the same value. For example

  it('utf8 test', () => {
     const input = Buffer.from([0x01, 0xff]);
     const [s, ] = readString(input, 0);
     const output = writeString(s);
     expect(input).toBe(output);
  });
  it('utf8 test 2', () => {
     const input = "ä";
     const input2 = "ä";
     const output = writeString(input);
     const output2 = writeString(input2);
     expect(Buffer.compare(output, output2)).toBe(0);
  });

Steps to reproduce

Add fuzz test to check random values