## Change Summary

This means `pydantic/__init__.py` is now lazy about all imports using `__getattr__`.

Import performance changes:
### Before

```
code/pydantic 0 ➤ pdm run python -m timeit -n 1 -r 1 "import pydantic"
1 loop, best of 1: 29.7 msec per loop
```

```
code/pydantic 0 ➤ pdm run python -m timeit -n 1 -r 1 "from pydantic import BaseModel"
1 loop, best of 1: 30.4 msec per loop
```

### After

```
code/pydantic 0 ➤ pdm run python -m timeit -n 1 -r 1 "import pydantic"
1 loop, best of 1: 4.8 msec per loop
```

```
(env3112) code/pydantic 0 ➤ pdm run python -m timeit -n 1 -r 1 "from pydantic import BaseModel"           
1 loop, best of 1: 18.7 msec per loop
```

Tuna output:

<img width="1421" alt="image" src="https://github.com/pydantic/pydantic/assets/4039449/0a57434e-fdda-4709-8793-d96c0a0ee762">

## Related issue number

As promised in https://github.com/pydantic/pydantic/pull/7423#issuecomment-1733361629.

## Checklist

* [x] The pull request title is a good summary of the changes - it will be used in the changelog
* [ ] Unit tests for the changes exist
* [x] Tests pass on CI
* [ ] Documentation reflects the changes where applicable
* [x] My PR is ready to review, **please add a comment including the phrase "please review" to assign reviewers**


Selected Reviewer: @sydney-runkle
Use `__getattr__` for all package imports, improve import time. ## Change Summary

This means `pydantic/__init__.py` is now lazy about all imports using `__getattr__`.

Import performance changes:
### Before

```
code/pydantic 0 ➤ pdm run python -m timeit -n 1 -r 1 "import pydantic"
1 loop, best of 1: 29.7 msec per loop
```

```
code/pydantic 0 ➤ pdm run python -m timeit -n 1 -r 1 "from pydantic import BaseModel"
1 loop, best of 1: 30.4 msec per loop
```

### After

```
code/pydantic 0 ➤ pdm run python -m timeit -n 1 -r 1 "import pydantic"
1 loop, best of 1: 4.8 msec per loop
```

```
(env3112) code/pydantic 0 ➤ pdm run python -m timeit -n 1 -r 1 "from pydantic import BaseModel"           
1 loop, best of 1: 18.7 msec per loop
```

Tuna output:

<img width="1421" alt="image" src="https://github.com/pydantic/pydantic/assets/4039449/0a57434e-fdda-4709-8793-d96c0a0ee762">

## Related issue number

As promised in https://github.com/pydantic/pydantic/pull/7423#issuecomment-1733361629.

## Checklist

* [x] The pull request title is a good summary of the changes - it will be used in the changelog
* [ ] Unit tests for the changes exist
* [x] Tests pass on CI
* [ ] Documentation reflects the changes where applicable
* [x] My PR is ready to review, **please add a comment including the phrase "please review" to assign reviewers**


Selected Reviewer: @sydney-runkle
[build-system]
requires = ["poetry>=0.12"]
build_backend = "poetry.masonry.api"

[tool.poetry]
name = "test"
version = "0.0.1"
readme = "README.md"
authors = [
    "author@example.com"
]

[tool.poetry.dependencies]
python = "*"

[tool.pytest.ini_options]
addopts = "-v -p no:warnings"

[tool.mypy]
plugins = [
    "pydantic.mypy"
]
follow_imports = "silent"
strict_optional = true
warn_redundant_casts = true
warn_unused_ignores = true
disallow_any_generics = true
check_untyped_defs = true
no_implicit_reexport = true
disallow_untyped_defs = true

[tool.pydantic-mypy]
init_forbid_extra = "foo"  # this will raise a ValueError for the config

[[tool.mypy.overrides]]
module = [
    'pydantic_core.*',
]
follow_imports = "skip"

[build-system]
requires = ["poetry>=0.12"]
build_backend = "poetry.masonry.api"

[tool.poetry]
name = "test"
version = "0.0.1"
readme = "README.md"
authors = [
    "author@example.com"
]

[tool.poetry.dependencies]
python = "*"

[tool.pytest.ini_options]
addopts = "-v -p no:warnings"

[tool.mypy]
plugins = [
    "pydantic.mypy"
]
follow_imports = "silent"
strict_optional = true
warn_redundant_casts = true
warn_unused_ignores = true
disallow_any_generics = true
check_untyped_defs = true
no_implicit_reexport = true
disallow_untyped_defs = true

[tool.pydantic-mypy]
init_forbid_extra = "foo"  # this will raise a ValueError for the config

[[tool.mypy.overrides]]
module = [
    'pydantic_core.*',
]
follow_imports = "skip"
