fix: quiet expected postgres error recovery

[f0rr0]

Summary

• demote expected PostgreSQL ERROR unwind recovery from WARN to debug logging
• add a regression covering PostgreSQL 17 gen_random_uuid() and recoverable uuidv4() SQLSTATE 42883 behavior
• add a README callout that the packaged runtime is based on PostgreSQL 17.5 and points users to gen_random_uuid()

Verification

• RUST_LOG=pglite_oxide::pglite::postgres_mod=warn cargo test pg17_uuidv4_alias_error_is_recoverable --test postgres_regression -- --nocapture
• pre-push hooks: git diff --check, cargo fmt, asset input fingerprint, example lockfiles, cargo check