feat: support readable time values in config

[l4l]

Human-readable durations in config

Time settings now accept strings like "1h5m15s" alongside plain numbers, so ban_timeout = 300000 can be written as ban_timeout = "5m".
Motivation: make these value readable by mere mortals.
The spaces can be put anywhere, so " 1 h 2 m " also should work. The plain numbers still work and handled as before, this is an extension for params view.

New pgdog-config/src/duration.rs parses ms/s/m/h/d via serde(with=..) for all time fields. PGDOG_* env vars supports the same syntax.

Limitations:

• only single symbol for easier parsing ("1s" works but not "1sec");
• no support for admin commands like SET ban_timeout TO '5m';
• only integers (i.e no "1.5s");

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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