Translate Length on Int32Range and Int64Range #405

Problem

Length on Int32Range and Int64Range runs in memory only (docs/efcore.md#what-runs-where), so a query can't filter or order by it. The obstacle the docs gave until #402 (that int4range overflows before a cast can widen it) doesn't hold: casting first works.

Change

Translate Length on both types to a scalar the server evaluates, matching memory exactly:

• Int32Range (long?): CASE WHEN isempty(x) THEN 0 ELSE upper(x)::bigint - lower(x)::bigint END. An unbounded side gives NULL because upper/lower do, which is memory's null. Measured on PostgreSQL 16: 4294967295 for [-2147483648,2147483647), 0 for empty, NULL for [1,). PostgreSQL's canonical [) form makes upper - lower the count memory returns ([1,10] measures 10).
• Int64Range (long?): memory computes in decimal and returns null when the count exceeds long.MaxValue. The SQL has to do the same: numeric arithmetic, and NULL above 9223372036854775807, never an int8 overflow error or a wrapped value.
• Declared nullability: NULL for a NULL range too (rule (c), a value-producing member over NULL).

Done when

Every condition on the 10.3.0 epic's parity list holds for both types: empty and unbounded shapes, the domain extremes, a nullable column and an outer-join operand, Where, OrderBy, a final Select (which ran in memory before) and a composed predicate (Length > n with &&/!), each against memory over the loaded rows on a live server. translation-support.json (#384) classifies both server, and the docs move the row to "Runs as SQL". main first, then the cherry-pick to release/10.x.