chore: complete google-cloud-bigtable migration

[jskeet]

It looks like this hadn't been regenerated with the latest version of the GAPIC generator (or at least not reformatted afterwards).

Fixes googleapis/librarian#5331

[gemini-code-assist]

Code Review

This pull request performs a significant cleanup and reformatting of imports across the Google Cloud Bigtable library, including several auto-generated files. Key functional changes include updating the AutomatedBackupPolicy in the admin API to support a new locations field and an expanded retention period range (3 to 90 days). Additionally, license headers were added to several test proxy proto files, and the repository metadata was streamlined. Feedback is provided regarding a minor typo in the documentation for the newly added locations field.

[gemini-code-assist]

There is a typo in the docstring for the locations field. It should be "can only be set" instead of "can only set".

Suggested change

	``projects/{project}/locations/{zone}``. This field can only
	set for tables in Enterprise Plus instances.
	projects/{project}/locations/{zone}. This field can only
	be set for tables in Enterprise Plus instances.

[parthea]

One of the unit tests failed with AssertionError: Found differences. Run nox -s generate_sync to update:. See the nox session here:

google-cloud-python/packages/google-cloud-bigtable/noxfile.py

Lines 552 to 558 in 9f0b3d7

	def generate_sync(session):
	"""
	Re-generate sync files for the library from CrossSync-annotated async source
	"""
	session.install(BLACK_VERSION)
	session.install("autoflake")
	session.run("python", ".cross_sync/generate.py", ".")

We may need to update the following code to switch from black to ruff

google-cloud-python/packages/google-cloud-bigtable/.cross_sync/generate.py

Lines 59 to 65 in 9f0b3d7

	import black # type: ignore
	import autoflake # type: ignore
	full_str = black.format_str(
	autoflake.fix_code(full_str, remove_all_unused_imports=True),
	mode=black.FileMode(),
	)

We may be able to remove the code formatting in the nox session if it's being done by the librarian. I don't have a lot of context on this code. cc @daniel-sanche

[parthea]

Switching to draft until checks are green