feat(spanner): log client configuration at startup

[sinhasubham]

This change introduces logging for Spanner client options upon initialization.

This allows customers to easily capture and inspect the configuration being used, which is valuable for debugging and verification.

This feature mirrors the existing logSpannerOptions functionality in the Java client, improving consistency across client libraries. googleapis/java-spanner#4141

[gemini-code-assist]

Summary of Changes

Hello @sinhasubham, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new feature to the Spanner client library that logs its configuration details upon initialization. This enhancement aims to improve the user experience by providing immediate and clear insight into the client's operational parameters, which is invaluable for diagnosing issues and confirming desired settings. The change also contributes to greater consistency across Google Cloud client libraries by mirroring functionality already present in the Java Spanner client.

Highlights

• Client Configuration Logging: Implemented logging of Spanner client options during initialization to provide immediate visibility into the client's setup.
• Enhanced Debugging and Verification: Enables easier debugging and verification of client configurations for users by exposing critical setup parameters.
• Cross-Client Consistency: Aligns the Python client's behavior with the existing logSpannerOptions functionality found in the Java client library, promoting consistency across client ecosystems.

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[gemini-code-assist]

Code Review

This pull request introduces logging for Spanner client options at startup, which is a great enhancement for debuggability. The implementation is mostly solid, and the tests are comprehensive. However, I've found a critical bug due to a function name typo that will cause a NameError on client initialization. I've also provided a suggestion to improve the clarity of the host resolution logic. Once the critical issue is addressed, this will be a valuable addition.

[gemini-code-assist]

There's a typo in the function call _get_spanner_enable_builtin_metrics(). The correct function name, as defined in this file, is _get_spanner_enable_builtin_metrics_env(). This typo will cause a NameError when a Client instance is initialized.

Suggested change

	_get_spanner_enable_builtin_metrics(),
	_get_spanner_enable_builtin_metrics_env(),

[gemini-code-assist]

The logic to determine the host can be made clearer and more robust by using an if/elif/else structure. This explicitly shows the precedence of different host configurations (_experimental_host > _emulator_host > api_endpoint) and avoids potential confusion from sequential if statements.

Consider refactoring this block to something like:

if self._experimental_host:
    host = self._experimental_host
elif self._emulator_host:
    host = self._emulator_host
elif self._client_options and self._client_options.api_endpoint:
    host = self._client_options.api_endpoint
else:
    host = "spanner.googleapis.com"