BigQueryReadClient context manager enter returns incompatible type for to_dataframe()

[antongollbo123]

Environment
OS: macOS 15.7.2
Python: 3.10.18
google-cloud-bigquery: 3.4.2
google-cloud-bigquery-storage: 2.35.0

Description
When using BigQueryReadClient as a context manager and passing it to RowIterator.to_dataframe(), type checkers report an incompatible type error even though the code works correctly at runtime.

Steps to Reproduce
from google.cloud import bigquery, bigquery_storage

client = bigquery.Client()
result = client.query("SELECT 1").result()

with bigquery_storage.BigQueryReadClient() as storage_client:
df = result.to_dataframe(bqstorage_client=storage_client)

Type Error
Argument "bqstorage_client" to "to_dataframe" of "RowIterator" has incompatible type "google.cloud.bigquery_storage_v1.services.big_query_read.client.BigQueryReadClient"; expected "google.cloud.bigquery_storage_v1.BigQueryReadClient | None"

Root Cause
The enter method's return type in the type stubs references the internal class path:
Annotated return type: google.cloud.bigquery_storage_v1.services.big_query_read.client.BigQueryReadClient
Expected by to_dataframe(): google.cloud.bigquery_storage_v1.BigQueryReadClient
At runtime, both resolve to the same class and enter correctly returns self. The issue is purely in the type annotations.

Verification
from google.cloud import bigquery_storage
from google.cloud.bigquery_storage_v1.services.big_query_read.client import BigQueryReadClient as InternalClient
from google.cloud.bigquery_storage_v1 import BigQueryReadClient as V1Client

print(bigquery_storage.BigQueryReadClient is V1Client) # True
print(V1Client is InternalClient) # False - different classes in type system

Expected Behavior
No type error when using BigQueryReadClient as a context manager and passing it to to_dataframe().

Workaround
Adding # type: ignore[arg-type] to suppress the false positive.