Refactor to use singledispatch `send_email()` and `to_email()`

[machow]

send_email()

# maybe clients.py ----
@dataclass
class Gmail:
    username: str
    password: str

@dataclass
class Smtp:
    host: str
    port: int
    username: str
    password: str
    security: str # Literal


# egress.py ----

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from typing import overloads as dispatch
else:
    from ddispatch import dispatch


@dispatch
def send_email(client: Gmail, i_email):
    ...
    # logic here...
    

@dispatch
def send_email(client: Smtp, i_email):
    ...
    # logic here...

to_email()

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from typing import overloads as dispatch
else:
    from ddispatch import dispatch

from email.message import EmailMessage
from .mjml import MJMLTag

@dispatch
def to_email(msg: EmailMessage):
    ...

@dispatch
def to_email(MJMLTag):
    ...