feat: update pydantic to v2; add pydantic-settings

[aekasitt]

This pull request is a divergence away from the last two pull requests that pins down Pydantic version to V1 but instead updates to PydanticV2 with all of its added benefits and adds pydantic-settings for its BaseSettings class over deprecated one.
.
Other changes:

• Replace deprecated "root_validator" decorators with "field_validator"
• Replace this deprecated syntax:

from pydantic import BaseModel
class Example(BaseModel):
    __root__: ...

with

from pydantic import RootModel
class Example(RootModel):
    root: ...

PS. Since the minimum required version is now Python 3.10, I suggest a project-wide change of change this 3.9 syntax using typing.Optional as well:

from pydantic import BaseModel
from typing import Optional
class Example(BaseModel):
    value: Optional[str]  # pydantic v1

to

from pydantic import BaseModel
class Example(BaseModel):
    value: None | str = None  # with pydantic v2, nullable syntax is more strict

or

from pydantic import BaseModel, Field
class Example(BaseModel):
    value: None | str = Field(default=None)  # with pydantic v2, nullable syntax is more strict

[callebtc]

Hi, thank you for the PR! I researched pydantic v2 before and it seemed a lot less performant. did you try any benchmarks?

[aekasitt]

Good idea. I found this closed issue on Pydantic codebase not yet fully resolved but going in a good direction:

• Pydantic v2 significantly slower than v1 pydantic/pydantic#6748

One of the participants made a good benchmark harness so I made a fork of it:

• marcodlk/pydantic-v2-startup-perf-bench

The fork is here as well as the results from my mac; expanding to the most up-to-date Pydantic V2 version.

• aekasitt/pydantic-v2-startup-perf-bench

Here are the benchmarks: