Add support for FreeCustom.Email temporary email provider

[DishantSinghDev2]

Is your feature request related to a problem? Please describe.
When generating accounts automatically, temporary email providers can sometimes become unavailable due to downtime, API changes, or domain blacklisting. Because of this, automation libraries benefit from supporting multiple disposable email providers so users can easily switch between them.

Currently this library supports several providers like TempMail, TempMail+, GmailNator, and InboxKitten. Adding another provider could improve reliability and flexibility for users running automated account generation or testing signup flows.

Describe the solution you'd like
Add support for FreeCustom.Email as an additional temporary email provider.

FreeCustom.Email provides disposable inboxes and has an official Python SDK (freecustom-email) which simplifies integration.

PyPI package:

pip install freecustom-email

Example usage:

import asyncio
from freecustom_email import FreeCustomEmail

async def main():
    client = FreeCustomEmail(api_key="fce_your_api_key")

    inbox = "signup-test@ditmail.info"
    await client.inboxes.register(inbox)

    print("Waiting for OTP...")
    otp = await client.otp.wait_for(inbox)

    print("Verification code:", otp)

asyncio.run(main())

Because an SDK already exists, adding support to this library should be relatively straightforward.

Describe alternatives you've considered
Users can currently rely on providers like TempMail or GmailNator. However, these services can sometimes stop working or become blocked by certain platforms. Adding additional providers gives users more options and redundancy.

Additional context
FreeCustom.Email documentation:
https://www.freecustom.email/api/docs

Python SDK documentation:
https://www.freecustom.email/api/docs/sdk/python

The service also supports automation workflows and disposable inbox creation via API, which fits well with the purpose of this project.

If you’re open to it, I’d be happy to contribute an implementation.