Go driver v0.1.2: bounded metadata discovery and TIMESTAMP parity

This release adds bounded, operator-authorized BigQuery metadata observation and initial discovery. Discovery returns partial public metadata; it does not create an executable source profile or submit a query job.

It also aligns typed TIMESTAMP query parameters with the shared Go/JavaScript request contract, including scalar and array values. The deadline test fixes retain the existing execution limits and no-late-dispatch checks.

Validated on Go 1.27 with race tests, vet, and formatting checks on Linux, macOS, and Windows. Provider access, billable queries, and live browser acceptance remain separate integration gates.