test(bigquery-jdbc): add picosecond timestamp integration tests

[keshavdandeva]

b/556664087

This PR adds ITs and and fixes one gap the ITs uncovered.

Production fix

BigQueryConnection.getBigQueryConnection() now sets
DataFormatOptions.TimestampFormatOptions.ISO8601_STRING when
EnableTimestampPicos=1.

The REST JSON read path was silently truncating to microseconds. BigQuery
serializes TIMESTAMP as FLOAT64 epoch seconds by default, which cannot
represent sub-microsecond digits; ISO8601_STRING is the only output format
that carries the full 12-digit fraction. The Arrow path was already correct,
which is why unit tests and metadata assertions passed while REST values did
not.

Gated on the property so the wire format is unchanged for existing users.

Tests

New ITJdbcTimestampPicosTest (11 tests): Arrow and REST read paths, complex
types (ARRAY/STRUCT), ResultSetMetaData, DatabaseMetaData.getColumns,
PreparedStatement round trips, Legacy SQL rejection, and timezone
invariance.

Registered in the presubmit, nightly, and driver-agnostic suites. Six tests
carry @Tag("advanced") where behavior is driver-specific; the remaining five
were verified to pass against other drivers.

Known limitation

BigQuery truncates TIMESTAMP-typed query parameters to microseconds even
against a TIMESTAMP(12) column (b/419328655), so setTimestamp/setObject
cannot write picosecond values. setString works, since the value is coerced
server side. Documented in USER_GUIDE.md and asserted in the tests so the
expectations flip loudly when the backend fix lands.

[gemini-code-assist]

Code Review

This pull request adds support for 12-digit picosecond precision for TIMESTAMP(12) data types in the BigQuery JDBC driver when EnableTimestampPicos is enabled, configuring DataFormatOptions to use ISO8601_STRING serialization. The changes include documentation updates, unit tests, and comprehensive integration tests. The reviewer suggested using a UUID-based suffix instead of a random integer for test table names to prevent potential collisions in concurrent CI/CD pipelines.