probe-output.schema: hold limit.unit and cost.unit to the contract's RESOURCE_UNITS (a subset test) #121

limit.unit (s, ms, bytes, count, us) and cost.unit (the constant ns-per-sample) are plugin-hostd's own lists (#120 left them so). Each word is a word of the contract's RESOURCE_UNITS today, so nothing has drifted. Add a test (about ten lines, in tests/vocabulary_derived.py) that every word of both is a word of the installed contract's RESOURCE_UNITS, with a positive control, so a unit the core lacks fails. Ruling: coordinator, 2026-10-20 (comment on #120).