Parse and serialize timestamp infinity as Infinity - fixes #728

[spokodev]

timestamptz/timestamp/date columns can hold the special values infinity and -infinity — e.g. expires timestamptz DEFAULT 'infinity' for "never expires". Postgres.js currently parses these through new Date('infinity'), which yields an Invalid Date: .getTime() is NaN, so every subsequent date comparison silently breaks. Reported in #728 (with a second report confirming it).

node-postgres maps these to JS Infinity / -Infinity (via postgres-date). This brings postgres.js in line.

Change (src/types.js, date type)

• parse: 'infinity' → Infinity, '-infinity' → -Infinity, otherwise new Date(x) as before.
• serialize: Infinity → 'infinity', -Infinity → '-infinity', otherwise unchanged. Without this half, writing a parsed Infinity back through the date serializer hits new Date(Infinity).toISOString(), which throws RangeError: Invalid time value — the two halves together let the value round-trip.

Behavior change (intentional)

Reading an infinity timestamp now returns the number Infinity instead of an Invalid Date. Code doing row.col.getTime() was already getting NaN; it now gets a value that compares correctly (Infinity > anyDate). This matches node-postgres and the underlying Postgres semantics.

Tests

Added alongside the existing Date cases — parse of 'infinity'/'-infinity', plus round-trip via sql.typed(±Infinity, 1184). Verified failing on main (parse → Invalid Date, round-trip → RangeError) and passing after the change; the normal Date path is unaffected.

Refs: Postgres date/time special values, node-postgres / postgres-date.