deps: Entend postgrex to 0.22.0

[MonsignorEduardo]

Extend postgrex to 0.22.0, increasing the minimum required elixir version to 1.15 also improved the CI.

This is the IA summary if you want

Summary

• Extends postgrex compatibility to include ~> 0.22.0.
• Raises the minimum supported Elixir version from ~> 1.14 to ~> 1.15, required by newer Postgrex versions.
• Refreshes mix.lock for Postgrex 0.22.1 and related dependency updates.
• Improves CI by adding format checks, explicit Elixir/OTP version jobs, compile-before-test validation, dependency/build caching, and Node 24-compatible GitHub Actions.
• Adds /.elixir_ls/ to .gitignore.

Validation

• CI now checks formatting on Elixir 1.19 / OTP 28.
• CI compiles and tests against:
  • Elixir 1.15 / OTP 24
  • Elixir 1.16 / OTP 26
  • Elixir 1.19 / OTP 28
    Note: the current PR body says minimum Elixir 1.5; it should be 1.15.