10.x: read an exclusive infinite date bound as memory loads it (port of #489) #502

Problem

On release/10.x, LowerBound(), UpperBound() and Clamp in a query read a date range another tool wrote with an exclusive infinite bound one day wider than memory loads it (#489). ClampFunction there reads the same UpperBoundFunction (upper(x) - 1) and lower(x) as on main, read at 61308c6. 10.4.0's own changelog says Clamp "answers as memory does, at the extremes too", and #494 made Clamp on DateRange and LocalDateRange run as SQL in this release, so without the port 10.4.0 ships a new disagreement next to a release note that denies it.

Change

Cherry-pick #489's fix commits from main with -x into a PR against release/10.x: the bound readers, their translation and live tests, and the docs.

10.x specifics: the changelog row goes under ### Changed answers in [10.4.0], linking #489 and its migration section. docs/migration.md lists that section under ## Changed answers in 10.4.0, beside #496's. pr-hygiene.sh requires both for a silent PR into a minor.

Done when

On release/10.x, the tests pass on the EF Core 10.0.0 floor and on CI's newest-patch leg, on PostgreSQL 16 and 18, and fail with the fix reverted.

Release

### Changed answers in 10.4.0. Fixed only on release/10.x, so close it by hand.