feat(bigquery-jdbc): optimize memory footprint for JSON result set streaming

[Neenu1995]

b/529436374

• Centralizes row-unpacking logic into BigQueryFieldValueListWrapper using a static, stateless utility pattern to reduce object allocations during JSON result set parsing.
• Pre-computes complex column flags (ARRAY, STRUCT, RANGE) outside the page-fetching loop in BigQueryStatement to avoid redundant per-row inspection.
• Preserves raw FieldValue references for complex types (RANGE, ARRAY, STRUCT) during row unpacking to prevent improper string coercion.

[gemini-code-assist]

Code Review

This pull request introduces BigQueryJsonStreamParser to parse BigQuery REST JSON responses into lightweight Object[] row buffers, reducing JVM heap overhead and GC pause times. It also updates BigQueryFieldValueListWrapper and BigQueryStatement to support and utilize these lightweight row buffers. The review feedback highlights critical infinite loop vulnerabilities in the JSON parsing loops when handling truncated or abruptly ended streams, and suggests using standard Jackson parsing patterns with explicit null token checks. Additionally, the reviewer recommends chaining constructors to reduce code duplication and removing unused stream parsing methods from the production code.

[logachev]

We already pass schema.getFields(), so we can just move isComplexColumn to be a part of BigQueryFieldValueListWrapper.of()? So no changes in statement, changes are scoped to the object itself

[Neenu1995]

BigQueryFieldValueListWrapper.of() is called once per row. Computing isComplexColumn that many times can be costly. It is ideal to call isComplexColumn once per query. Hence the current design.

I will keep the isComplexColumn in Statement but can eliminate the other change by reusing the of method instead of creating a new ofUnpackedRow method.