community[patch]: Upgrade pydantic extra (#25185)

Upgrade to using a literal for specifying the extra which is the
recommended approach in pydantic 2.

This works correctly also in pydantic v1.

```python
from pydantic.v1 import BaseModel

class Foo(BaseModel, extra="forbid"):
    x: int

Foo(x=5, y=1)
```

And 


```python
from pydantic.v1 import BaseModel

class Foo(BaseModel):
    x: int

    class Config:
      extra = "forbid"

Foo(x=5, y=1)
```


## Enum -> literal using grit pattern:

```
engine marzano(0.1)
language python
or {
    `extra=Extra.allow` => `extra="allow"`,
    `extra=Extra.forbid` => `extra="forbid"`,
    `extra=Extra.ignore` => `extra="ignore"`
}
```

Resorted attributes in config and removed doc-string in case we will
need to deal with going back and forth between pydantic v1 and v2 during
the 0.3 release. (This will reduce merge conflicts.)


## Sort attributes in Config:

```
engine marzano(0.1)
language python


function sort($values) js {
    return $values.text.split(',').sort().join("\n");
}


class_definition($name, $body) as $C where {
    $name <: `Config`,
    $body <: block($statements),
    $values = [],
    $statements <: some bubble($values) assignment() as $A where {
        $values += $A
    },
    $body => sort($values),
}

```

libs/community/langchain_community/tools/searx_search/tool.py

@@ -6,7 +6,7 @@ from langchain_core.callbacks import (
     AsyncCallbackManagerForToolRun,
     CallbackManagerForToolRun,
 )
-from langchain_core.pydantic_v1 import BaseModel, Extra, Field
+from langchain_core.pydantic_v1 import BaseModel, Field
 from langchain_core.tools import BaseTool
 
 from langchain_community.utilities.searx_search import SearxSearchWrapper
@@ -62,9 +62,7 @@ class SearxSearchResults(BaseTool):
     kwargs: dict = Field(default_factory=dict)
 
     class Config:
-        """Pydantic config."""
-
-        extra = Extra.allow
+        extra = "allow"
 
     def _run(
         self,