fix: SQLite3 config type handling for .env overrides

[michalsn]

Description
This PR fixes a bug where database config values coming from .env could remain strings and then be assigned to typed SQLite3 connection properties with the wrong type. That could trigger a TypeError for synchronous or cause busyTimeout to be ignored.

The fix normalizes string config values when they are assigned to typed connection properties, and also types SQLite3\Connection::$busyTimeout as ?int so it behaves consistently. This is done in BaseConnection, where the real destination type is known, rather than trying to guess types for null values in config arrays.

Fixes#10021

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[paulbalandan]

Why is this fix only targeting database connections? Should other core classes that declare typed properties in the future be affected by the bug and thus deserve also to be fixed?

[michalsn]

This fix targets database connections because that's the actual bug we have today.

There's no safe global fix for all cases. Mixed config arrays are the problem: null entries don't carry type information, so there's no universal way to know what they should become. The right place to handle that is at the consumer boundary, where the destination property type is known.

Although I'm open to ideas.

[neznaika0]

Thanks for the PR. This fixes the problem, but I personally don't really like the extra checks with reflection. I can't offer you anything better.

[michalsn]

Well, the only other option I see is removing the ability to assign null to these values altogether - but that would probably be a bigger BC break than this.

[michalsn]

Okay, this is fine for now unless we find a better approach.

Thanks for the reviews!