[FEATURE]: Bulk update using values

### Describe the enhancement you want to request

Being able to bulk update multiple rows in one statement using values, similar to how you can bulk insert in one statement using values, would be great. The main motivations are performance and avoiding problems with swapping values of a unique column, which breaks if done sequentially regardless of order.

See this stackoverflow question for the desired syntax on the SQL side: https://stackoverflow.com/questions/18797608/update-multiple-rows-in-same-query-using-postgresql

Currently it seems the easiest approach is to just use `db.execute(sql...)` despite losing all the usual benefits of a type safe sql builder.

The issue names no files or tests. Start by reading the existing bulk-insert and values-building support, then compare it with the db.execute(sql...) path and the linked PostgreSQL syntax. Done means multiple rows can be updated in one statement through the type-safe SQL builder, including swaps of unique-column values.

Written by the indexing model from the issue text.