Fix Parquet writes for multi-record Avro unions

[freeznet]

Problem

Generic Avro conversion always selected the first record branch in a union. Records using a later branch could therefore be converted with an incompatible schema before being written to Parquet.

Changes

• Resolve the concrete union branch from the native Avro record schema.
• Preserve the existing fallback for nullable unions with one record branch.
• Fail explicitly when a multi-record branch cannot be determined.
• Add a Parquet round-trip regression test for a non-first record branch with an incompatible nested field type.
• Align the regression test with the repository Checkstyle rules.
• Update dependency overrides required by the repository vulnerability scan.

Validation

• JAVA_HOME=/path/to/jdk17 mvn -B -ntp clean license:check checkstyle:check spotbugs:check
• JAVA_HOME=/path/to/jdk17 mvn -B -ntp -Dtest=ParquetMultiRecordUnionTest test
• trivy fs --scanners vuln --severity CRITICAL,HIGH --exit-code 1 --timeout 10m .

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[github-actions]

@freeznet:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)