PostgreSQL: Handle timestamp edge cases

[dtsong]

Problem

data_diff/databases/postgresql.py:144,162 — Timezone overflow and years >9999 not handled.

Impact

Edge case failures when comparing extreme timestamp values.

Suggested Fix

Add boundary checks for timezone overflow and extended year ranges.

References

• File: data_diff/databases/postgresql.py, lines 144, 162

[dtsong]

PostgreSQL timestamp edge cases were fixed in PR #20 (commit 33f22a9) with robust datetime parsing.