chore(main): release 6.91.0

[release-please]

🤖 I have created a release beep boop

6.91.0 (2025-04-17)

Features

• [Internal] open telemetry built in metrics for GRPC (#3709) (cd76c73)
• Add java sample for the pre-splitting feature (#3713) (e97b92e)
• Add TransactionMutationLimitExceededException as cause to SpannerBatchUpdateException (#3723) (4cf5261)
• Built in metrics for afe latency and connectivity error (#3724) (e13a2f9)
• Support unnamed parameters (#3820) (1afd815)

Bug Fixes

• Add default implementations for Interval methods in AbstractStructReader (#3722) (97f4544)
• Set transaction isolation level had no effect (#3718) (b382999)

Performance Improvements

• Cache the key used for OTEL traces and metrics (#3814) (c5a2045)
• Optimize parsing in Connection API (#3800) (a2780ed)
• Qualify statements without removing comments (#3810) (d358cb9)
• Remove all calls to getSqlWithoutComments (#3822) (0e1e14c)

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[release-please]

🤖 Created releases:

• v6.91.0

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Triggered job: cloud-devrel/client-libraries/java/java-spanner/release/stage (2025-04-21T06:13:15.800Z)

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