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 <tsechkova@vmware.com>

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