base58 decoding: parsing byte size

[akinwilson]

In the Base58 decode function here, the integer is parsed into 25 bytes

i.e.

def decode_base58(s):
    num = 0
    for c in s:  # <1>
        num *= 58
        num += BASE58_ALPHABET.index(c)
    combined = num.to_bytes(25, byteorder='big')  # <2>
    checksum = combined[-4:]
    if hash256(combined[:-4])[:4] != checksum:
        raise ValueError('bad address: {} {}'.format(checksum, 
          hash256(combined[:-4])[:4]))
    return combined[1:-4]  # <3>

Why is the value 25 bytes chosen as a container size for the decoded value?

when I define a Base58 class, like

class Base58:
    SYMBOLS = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
    ORDER = SYMBOLS.__len__()  # aka cardinality
    def encode(s: bytes):
        # Counting leading zeros 
        # 
        count = 0
        for c in s:
            if c == 0:
                count += 1
            else:
                break
        
        num = int.from_bytes(s, "big")
        # adding leading zeros in base58 representation (1s), back    
        prefix = Base58.SYMBOLS[0] * count
        result = ""
        while num > 0:
            num, mod = divmod(num, Base58.ORDER)
            result = Base58.SYMBOLS[mod] + result
        return prefix + result


    def decode(s):
        num = 0
        for c in s:
            num *= Base58.ORDER # increment the value each digit placeholder can hold
            num += Base58.SYMBOLS.index(c)
        return f"{num:x}"

and then test the encoding and decoding scheme with

b16 = '7c076ff316692a3d7eb3c3bb0f8b1488cf72e1afcd929e29307032997a838a3d'

def test_base58_encoding(x):
    a = bytes.fromhex(x)
    return Base58.encode(a)


def test_base58_decoding(x):
    return Base58.decode(x)


b58 = test_base58_encoding(b16)

b16 == test_base58_decoding(b58)

it evaluates to be true, so what is the purpose of parsing the in the integer into a 25 byte container?