feat(bigframes): Gcs bucket read will bind to gcs region if region unset

[TrevorBergeron]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request implements automatic BigQuery location detection based on GCS bucket locations for various read functions and from_glob_path. It introduces a helper function to retrieve a storage client and logic to set the default session location if it hasn't been explicitly configured. Review feedback highlights a missing threading import and lock definition in the API module, as well as a case-sensitivity error in the new unit tests' assertions.

[gemini-code-assist]

The variable _default_location_lock is used but not defined at the module level, and the threading module is not imported in this file. This will result in a NameError at runtime when _set_default_session_location_if_possible_gcs is called. Please define the lock at the module level (e.g., _default_location_lock = threading.Lock()) and ensure threading is imported.

[gemini-code-assist]

The assertion expects "EU", but the location was set to "eu" at line 161. Since _set_default_session_location_if_possible_gcs returns early when a location is already set, the value will remain "eu", causing this test to fail. Based on the previous test case (line 148), locations appear to be case-sensitive in these assertions.

Suggested change

	assert config.options.bigquery.location == "EU"
	assert config.options.bigquery.location == "eu"