Accomodating oauth2client moves of GCE/App Engine modules.

Source-Link: googleapis/synthtool@db94845
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:a8a80fc6456e433df53fc2a0d72ca0345db0ddefb409f1b75b118dfd1babd952

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: Anthonios Partheniou <partheniou@google.com>

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

Re-opening #1495 due to permissions issues.

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Fixes #<issue_number_goes_here> 🦕

---------

Co-authored-by: Knut Olav Løite <koloite@gmail.com>

PR created by the Librarian CLI to initialize a release. Merging this PR
will auto trigger a release.

Librarian Version: v0.0.0-20260331223231-14b1b9186e21
Language Image:
us-central1-docker.pkg.dev/cloud-sdk-librarian-prod/images-prod/python-librarian-generator@sha256:234b9d1f2ddb057ed7ac6a38db0bf8163d839c65c6cf88ade52530cddebce59e
<details><summary>google-cloud-spanner: v3.64.0</summary>

##
[v3.64.0](google-cloud-spanner-v3.63.0...google-cloud-spanner-v3.64.0)
(2026-04-01)

### Features

* use inline begin to eliminate BeginTransaction RPC (#1502)
([00d5f8e6](00d5f8e6))

* add TLS/mTLS support for experimental host (#1479)
([0c4c5da](0c4c5da3))

* add Client Context support to options (#1499)
([0da5f78](0da5f785))

* Exposing total CPU related fields in AutoscalingConfig
(PiperOrigin-RevId: 845819318)
([9d2338a](9d2338a6))

* include cache updates into the ResultSet response (PiperOrigin-RevId:
865546011)
([9d2338a](9d2338a6))

* add a ClientContext field to Spanner requests (PiperOrigin-RevId:
853323071)
([9d2338a](9d2338a6))

* include cache updates and routing hint into BeginTransaction and
Commit request/response respectively (PiperOrigin-RevId: 878019893)
([9d2338a](9d2338a6))

* add Secure Parameters to the ClientContext (PiperOrigin-RevId:
853323071)
([9d2338a](9d2338a6))

* implement native asyncio support via Cross-Sync (#1509)
([f822fd7](f822fd7c))

### Bug Fixes

* add threading import and _resource_info to snapshot.py
([659034a](659034aa))

* restore implicit database_dialect reload in sync client (#1537)
([67f5104](67f51043))

* resolve async deadlock in multiplexed session manager (#1520)
([c8f936b](c8f936b0))

### Documentation

* mark new AsyncIO APIs as experimental (#1533)
([3909c04](3909c045))

* A comment for field `transaction_tag` in message
`.google.spanner.v1.RequestOptions` is changed (PiperOrigin-RevId:
865546011)
([9d2338a](9d2338a6))

* A comment for field `routing_hint` in messages
`.google.spanner.v1.ResultSet` and `.google.spanner.v1.PartialResultSet`
are changed (PiperOrigin-RevId: 878019893)
([9d2338a](9d2338a6))

* Update high_priority_cpu_utilization_percent in AutoscalingConfig to
be Optional and clarify its behavior when not specified
(PiperOrigin-RevId: 845819318)
([9d2338a](9d2338a6))

* A comment for field `params` in message
`.google.spanner.v1.PartitionQueryRequest` is changed
(PiperOrigin-RevId: 865546011)
([9d2338a](9d2338a6))

* A comment in message
`.google.spanner.v1.TransactionOptions.ReadWrite.ReadLockMode` is
changed (PiperOrigin-RevId: 878019893)
([9d2338a](9d2338a6))

* A comment for field `commit_timestamp` in message
`.google.spanner.v1.BatchWriteResponse` is changed (PiperOrigin-RevId:
865546011)
([9d2338a](9d2338a6))

* minor update for Spanner Location API (PiperOrigin-RevId: 834841888)
([9d2338a](9d2338a6))

* A comment for field `param_types` in message
`.google.spanner.v1.PartitionQueryRequest` is changed
(PiperOrigin-RevId: 865546011)
([9d2338a](9d2338a6))

</details>

* fix: fix pandas.cut errors with empty bins

* nit

* refactor if branches for more readable