SQL misc functions (geo.buffer, date): adopt FunctionOptions for trailing options

[lvca]

Motivation

Final follow-up to #3881, #3882, and #3883. Two remaining candidates for the options-map pattern:

• geo.buffer(geom, distance) - JTS buffer() natively supports quadrantSegments, endCapStyle, joinStyle beyond the scalar distance. A trailing options map is the natural extension point.
• date([val [, format [, timezone]]]) - three positional optionals of mixed types. Growth likely (locale, strict).

Proposal

Accept a trailing options map validated by FunctionOptions on each. Positional forms remain supported. Unknown keys are rejected.

Deliverables

• Code: route trailing options through FunctionOptions.
• Tests: options-map path + unknown-key rejection.
• Docs: show options-map syntax.