Add type hints for IDEs

Extend the type annotations with ones not needed
by mypy but helping IDEs discover the return type of
Metadata.from_bytes and give correct hints and suggestions.

Signed-off-by: Teodora Sechkova <[email protected]>

Author: sechkova

tuf/ngclient/_internal/trusted_metadata_set.py

@@ -196,7 +196,7 @@ def update_root(self, data: bytes) -> None:
         logger.debug("Updating root")
 
         try:
-            new_root = Metadata[Root].from_bytes(data)
+            new_root: Metadata[Root] = Metadata[Root].from_bytes(data)
         except DeserializationError as e:
             raise exceptions.RepositoryError("Failed to load root") from e
 
@@ -261,7 +261,9 @@ def update_timestamp(self, data: bytes) -> None:
             raise RuntimeError("Cannot update timestamp after snapshot")
 
         try:
-            new_timestamp = Metadata[Timestamp].from_bytes(data)
+            new_timestamp: Metadata[Timestamp] = Metadata[Timestamp].from_bytes(
+                data
+            )
         except DeserializationError as e:
             raise exceptions.RepositoryError("Failed to load timestamp") from e
 
@@ -330,7 +332,9 @@ def update_snapshot(self, data: bytes) -> None:
             ) from e
 
         try:
-            new_snapshot = Metadata[Snapshot].from_bytes(data)
+            new_snapshot: Metadata[Snapshot] = Metadata[Snapshot].from_bytes(
+                data
+            )
         except DeserializationError as e:
             raise exceptions.RepositoryError("Failed to load snapshot") from e
 
@@ -429,7 +433,7 @@ def update_delegated_targets(
             ) from e
 
         try:
-            new_delegate = Metadata[Targets].from_bytes(data)
+            new_delegate: Metadata[Targets] = Metadata[Targets].from_bytes(data)
         except DeserializationError as e:
             raise exceptions.RepositoryError("Failed to load snapshot") from e