Post-1.0 hardening and support expansion

[quinnj]

PR #5 defines and tests a narrow 1.0 support boundary. This issue tracks useful work that is intentionally deferred until after the initial release.

• Apply connect_timeout to PostgreSQL authentication and the complete startup handshake.
• Give wait_for_notification a strict whole-message deadline, including trickled TCP input and resumable TLS polling.
• Preserve and dispatch notices and notifications that arrive during prepare, describe, bind, close, and other setup waits.
• Add explicit task ownership for manual transactions and streaming cursors, while keeping cancellation cross-task.
• Add protocol-safe dead-peer validation for pooled connections without retrying ambiguous user operations.
• Restore a zero-error JuliaC --trim executable gate before advertising native compilation support.
• Remove the TLS 1.2 client-certificate limit after the dependency sends mTLS certificates reliably on its mixed TLS path, and add IP-SAN verification coverage.
• Consider direct parameter binding for registered enum, composite, and range values, plus multidimensional arrays.
• Decide whether COPY helpers should use extended protocol so extra statements are rejected before any side effects.
• Define stronger behavior for date and interval formats after arbitrary mid-session SET operations and through transaction poolers.

None of these items is part of the documented 1.0 contract. The current boundary is in docs/src/support.md.