Replace standalone pgconn import with pgx/v5/pgconn

[Vad1mo]

dbtracer/dbtracer.go imports the standalone github.com/jackc/pgconn (pgx/v4-era module) while the rest of the library uses pgx/v5, where pgconn was folded into the main module.

Any project that uses sqlc-pgx-monitoring alongside pgx/v5 gets the standalone pgconn (and its transitive deps) pulled into their go.mod. This is problematic for projects that are migrating away from pgx/v4 and want a clean dependency graph with no v4 remnants.

The only workaround is a local patched copy with a replace directive.

Happy to submit a PR.

[amirsalarsafaei]

Hi, thanks for raising the issue.
A PR would be at most welcome.