google-cloud-bigquery: support python-dateutil 4.x #18948

Is your feature request related to a problem? Please describe.

Please add support for python-dateutil 4.x. Upgrading our application's direct dependency from python-dateutil==2.9.0.post0 to python-dateutil==4.0.0 is blocked by google-cloud-bigquery==3.47.0, which requires python-dateutil>=2.8.2,<3.0.0.

Both our Linux and Windows CI jobs fail during dependency resolution, before application checks or tests run. Renovate also reports that regeneration of uv.lock is blocked by this conflict.

The Linux job runs uv sync --locked; the Windows job runs uv sync --locked --no-build --no-cache --no-install-package brotli. Both report:

error: No solution found when resolving dependencies
  cause: Because google-cloud-bigquery>=3.47.0 depends on python-dateutil>=2.8.2,<3.0.0 and your project depends on google-cloud-bigquery==3.47.0, we can conclude that your project depends on python-dateutil>=2.8.2,<3.0.0.
         And because your project depends on python-dateutil==4.0.0, we can conclude that your project's requirements are unsatisfiable.

The relevant direct dependency entries are:

dependencies = [
    "google-cloud-bigquery==3.47.0",
    "python-dateutil==4.0.0",
]

Describe the solution you'd like

Please evaluate compatibility with python-dateutil 4.x, make any necessary code/test changes, and publish a release with a dependency range that permits it. If there are known incompatibilities that require retaining the upper bound, documenting those blockers would also help downstream users.

Describe alternatives you've considered

For now, we can retain python-dateutil==2.9.0.post0 and defer the upgrade. Regenerating the lockfile alone cannot resolve the contradictory requirements. We have not overridden the dependency bound or validated runtime compatibility with dateutil 4.

Additional context

This is a request for dependency support, not a report of a demonstrated runtime regression in either library: installation fails before tests execute.

Related: #18806 tracks the same upper-bound restriction for dateutil 3.0. This request specifically asks for evaluation of dateutil 4.x with google-cloud-bigquery 3.47.0.