Support Date encoding with sub-millisecond precision #484

Description

Currently, Date is recorded a String with millisecond precision (for most modern devices).

For applications expecting greater precision (e.g., Dates compared to nanosecond precision in existing logic), custom @Column and #bind work, but require dashes of ceremony everywhere.

Avoiding that ceremony is possible if these formatters could output by default (or as an option) with greater precision.

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• I have determined whether this bug is also reproducible in a vanilla GRDB project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

Record Date with same precision as default JSONEncoder/Decoder behavior.

Actual behavior

Rounded millisecond precision

SQLiteData version information

1.6.6