feat(bigquery-jdbc): add picosecond precision support for TIMESTAMP

[keshavdandeva]

b/544839231

This PR introduces support for picosecond precision (up to 12 fractional digits) when reading BigQuery TIMESTAMP columns, building on top of #14037

Overview

To maintain strict backwards compatibility, picosecond precision is disabled by default and activated via the new EnableTimestampPicos connection property:

• Disabled (default): Timestamps maintain standard 6-digit microsecond precision across metadata (displaySize=26, precision=26, scale=6), getString(), getTimestamp(), and getObject().
• Enabled on picosecond columns: Reports displaySize=32, precision=32, scale=12 in ResultSetMetaData and preserves full 12-digit picosecond precision in getString().

Changes Made

• Configuration:

  • Added the EnableTimestampPicos connection property in BigQueryConnection and DataSource.

• Arrow Storage Engine:

  • Configured ReadSession creation in BigQueryStatement to explicitly request TIMESTAMP_PRECISION_PICOS when EnableTimestampPicos is active.
  • Added type coercions for Text -> Timestamp and String -> Timestamp in BigQueryTypeCoercionUtility using BigQueryTemporalUtility::boxTimestamp so getObject() and getTimestamp() seamlessly handle Arrow picosecond VarCharVector columns.

• JDBC Metadata:

  • Updated BigQueryResultSetMetadata to report displaySize=32, precision=32, and scale=12 when EnableTimestampPicos is active and the column schema precision is 12.

• Temporal Utilities & API Safety:

  • boxTimestamp(): Gracefully down-casts 12-digit picosecond strings to 9 digits (nanoseconds) for java.sql.Timestamp, which maxes out at nanosecond precision and would otherwise throw a DateTimeParseException.
  • formatTimestampStringFromIso(): Standardized ISO-8601 formatting supporting both 'T'/'Z', SQL space-delimited (' '/' UTC'), and raw strings.

Testing

• Unit Tests:
  • Added mocked Arrow vector tests in BigQueryArrowResultSetTest verifying getString(), getTimestamp(), and getObject() against picosecond Text columns.
  • Added metadata tests in BigQueryResultSetMetadataTest verifying precision, scale, and display size with picoseconds enabled and disabled.
  • Added ISO-8601 coercions tests in ArrowFormatTypeBigQueryCoercionUtilityTest and BigQueryTemporalUtilityTest.

[gemini-code-assist]

Code Review

This pull request introduces support for 12-digit picosecond precision for TIMESTAMP columns in the BigQuery JDBC driver, controlled by a new connection property EnableTimestampPicos. It updates result set implementations, connection settings, statement processing, and metadata to handle picosecond precision when enabled. One high-severity issue was identified where the default value for the EnableTimestampPicos property is set to the string "false" instead of "0", which could cause parsing errors during connection initialization.

[logachev]

Can you update integration tests too? Probably tests that do format validation + tests your wrote a few weeks/months ago for picoseconds

[logachev]

nit: maybe using isWrapperFor/unwrap methods?