When editing / updating a GPKG `last_change` column in gpkg_contents isn't correctly upheld

**Describe the bug**

A clear and concise description of what the bug is.

**To Reproduce**

Run the `merger` on any `geopackage` to update it. The `last_change` field won't be updated.

**Expected behavior**

Either update `last_change` to be the time of the last write to the table, or to be the data's original creation date.

**Additional context**

The `last_change` column as described in [`geopackage` spec](https://www.geopackage.org/spec/):
> The last_change SHOULD contain the timestamp of when the content in the referenced table was last updated, in ISO8601 format. Note that since it is not practical to ensure that this value is maintained properly in all cases, this value should be treated as informative.

Start by running the merger on a GeoPackage and inspect the gpkg_contents last_change value before and after an update. Review the GeoPackage specification and the merger entry point to determine which timestamp behavior is intended; done means the chosen behavior is implemented and the updated value can be verified after a write.

Written by the indexing model from the issue text.