fix: Parse API Response to Avoid Nulls

[ppfenning]

Though the API response was returning field params, the Geocodio client was not parsing them correctly. Changes of note in this PR:

• acs and census fields return as a dictionary and are now parsed as such
• zip4 and ffiec are now parsed correctly
• CensusData, ZIP4Data and FFIECData now have keys matching their response
• GeocodioFields to include extras as not to lose response information from API call

[ppfenning]

This also mitigates problems raised in #12

[ppfenning]

Attaching an example result using the below:

from geocodio import Geocodio
from dotenv import load_dotenv
import os
import json
from dataclasses import asdict

# Load environment variables from .env file
load_dotenv()

client = Geocodio(os.getenv("GEOCODIO_API_KEY"), hostname=os.getenv("GEOCODIO_HOST"))

data = client.geocode(
    "3730 N Clark St, Chicago, IL",
    fields=[
        "cd",
        "timezone",
        "ffiec",
        "zip4",
        "acs-demographics",
        "acs-economic",
        "acs-housing", 
        "acs-social", 
        "acs-families", 
        "census2024"
    ]
)

with open('output.json', 'w') as f:
    f.write(json.dumps(asdict(data), indent=2))

output.json