pendulum DateTime type doesn't accept python standard datetime

[antti-ngp]

Glad the library includes the pendulum DateTime now. I was just starting to use it but noticed it doesn't accept the standard python datetime objects as expected.

Steps to reproduce:

from pydantic_extra_types.pendulum_dt import DateTime
import datetime
import pydantic

class MyTest(pydantic.BaseModel):
    my_pendulum_dt: DateTime

MyTest(my_pendulum_dt=datetime.datetime(2024,2,8,0,0,1))

Expected results:

MyTest(my_pendulum_dt=DateTime(2024, 2, 8, 0, 0, 1))

Actual results:

pydantic_core._pydantic_core.ValidationError: 1 validation error for MyTest
my_pendulum_dt
  value is not a valid timestamp [type=value_error, input_value=datetime.datetime(2024, 2, 8, 0, 0, 1), input_type=datetime]

Suggested fix:
Use pendulum.instance() for input of the type datetime.datetime before using pendulum.parse() for other types of input.

[07pepa]

@yezz123 this can be closed already present here with test and merged #176