Refactor: update validation for Pydantic v2

Changed @root_validator to @model_validator(mode="after") for checking data after the model is created.
Updated values to use a more flexible type for Pydantic v2.
Accessed values as a dictionary (values["payload"]) instead of using values.payload.

src/aleph/vm/orchestrator/views/authentication.py

@@ -22,7 +22,8 @@
 from jwcrypto import jwk
 from jwcrypto.jwa import JWA
 from nacl.exceptions import BadSignatureError
-from pydantic import BaseModel, ValidationError, field_validator, model_validator
+from pydantic import (BaseModel, ValidationError, ValidationInfo,
+                      field_validator, model_validator)
 from solathon.utils import verify_signature
 
 from aleph.vm.conf import settings
@@ -103,26 +104,23 @@ def payload_must_be_hex(cls, v: bytes) -> bytes:
         return bytes.fromhex(v.decode())
 
     @model_validator(mode="after")
-    @classmethod
-    def check_expiry(cls, values) -> dict[str, bytes]:
+    def check_expiry(values) -> 'SignedPubKeyHeader':
         """Check that the token has not expired"""
-        payload: bytes = values.payload
+        payload = values.payload
         content = SignedPubKeyPayload.model_validate_json(payload)
         if not is_token_still_valid(content.expires):
-            msg = "Token expired"
-            raise ValueError(msg)
+            raise ValueError("Token expired")
         return values
 
     @model_validator(mode="after")
-    @classmethod
-    def check_signature(cls, values) -> dict[str, bytes]:
+    def check_signature(values) -> 'SignedPubKeyHeader':
         """Check that the signature is valid"""
-        signature: list = values.signature
-        payload: bytes = values.payload
+        signature = values.signature
+        payload = values.payload
         content = SignedPubKeyPayload.model_validate_json(payload)
         check_wallet_signature_or_raise(content.address, content.chain, payload, signature)
         return values
-
+    
     @property
     def content(self) -> SignedPubKeyPayload:
         """Return the content of the header"""