fix(connections): unwrap optional session.driver in the metadata pool

[datlechin]

Problem

main does not compile after the PGlite PR (#1934). MetadataConnectionPool.acquireEntry uses session.driver (an optional DatabaseDriver?) as if it were non-optional:

guard session.driver.status == .connected else { throw DatabaseError.notConnected }
return Entry(driver: session.driver, ownsDriver: false)

error: Value of optional type '(any DatabaseDriver)?' must be unwrapped to refer to member 'status'
error: Value of optional type '(any DatabaseDriver)?' must be unwrapped to a value of type 'any DatabaseDriver'

Fix

Unwrap session.driver once with guard let, then use it for both the status check and the Entry. A session with no driver throws notConnected, matching the other paths in the pool.

Build fix only, no behavior change. #1934 is unreleased, so no CHANGELOG entry.

https://claude.ai/code/session_01FYwKEwKydeMG6WAHucMdY9