Enable use of idle connection pruning

[gwynne]

These changes are now available in 2.11.0

AsyncKit 1.21.0 added support for automatic pruning of idle database connections in the connection pool. This PR adds the necessary configuration parameters to the Postgres driver, enabling Fluent users to take advantage of this new functionality:

app.databases.use(.postgres(
    url: "postgres://user@pass:host/db",
    pruningInterval: .minutes(1),
    maxIdleTimeBeforePruning: .minutes(10)
), as: .psql)

The pruningInterval controls how often the pool will check for idle connections; specifying nil disables idle pruning entirely. The maxIdleTimeBeforePruning controls how long a connection must go unused before being pruned.

[codecov]

Codecov Report

❌ Patch coverage is 8.53659% with 75 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.23%. Comparing base (fd57101) to head (dc0d053).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ntPostgresDriver/FluentPostgresConfiguration.swift	6.25%	75 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #225      +/-   ##
==========================================
- Coverage   63.39%   54.23%   -9.16%     
==========================================
  Files           8        8              
  Lines         336      437     +101     
==========================================
+ Hits          213      237      +24     
- Misses        123      200      +77     

Files with missing lines	Coverage Δ
.../FluentPostgresDriver/FluentPostgresDatabase.swift	80.21% <100.00%> (-0.87%)	⬇️
...uentPostgresDriver/PostgresConverterDelegate.swift	88.09% <100.00%> (ø)
...ntPostgresDriver/FluentPostgresConfiguration.swift	20.68% <6.25%> (-16.08%)	⬇️

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