fix: retrying known incorrect passwords repeatedly

[levkk]

When configuring multiple passwords, PgDog would attempt the bad ones on every connection, even if a previous attempt would fail. We now track the password validity and attempt the known good password first. This decreases the number of incorrect password attempts substantially and won't get us banned by certain database hosting providers.

[codecov]

Codecov Report

❌ Patch coverage is 84.49612% with 40 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/stats/pools.rs	0.00%	26 Missing ⚠️
pgdog/src/backend/pool/password.rs	79.41%	7 Missing ⚠️
pgdog/src/backend/pool/test/mod.rs	97.70%	2 Missing ⚠️
pgdog/src/admin/show_stats.rs	0.00%	1 Missing ⚠️
pgdog/src/backend/auth/azure_workload_identity.rs	0.00%	1 Missing ⚠️
pgdog/src/backend/error.rs	83.33%	1 Missing ⚠️
pgdog/src/backend/pool/address.rs	98.52%	1 Missing ⚠️
pgdog/src/backend/server.rs	91.66%	1 Missing ⚠️

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