Group-stepwise ORDC, load reserve provision, and OfflineReserve ORDC supply - #236

PSY moved GroupReserve into the reserve tree, so the RESERVE_PRODUCT_TYPES
alias and the per-type methods that existed only because groups sat outside
it are gone: every former Union bound is plain PSY.AbstractReserve, the
group get_initial_conditions_service_model and the CostExpressions container
sibling fold into the AbstractReserve methods, and uses_compact_power opens
to the abstract type. Formulation-pair bounds
(Union{StepwiseCostReserve, GroupStepwiseCostReserve}) and the group demand
predicates stay - they encode formulation semantics, not typing.

The pairing guards merge with the #235 hardening set: valid direction-applied
pairs for both group formulations, the generic-defaults disambiguator, the
inverse guard over both formulations, and a direction-required error for
bare GroupReserve declarations.

A controllable load routes reserves inversely to generators: up reserve
is committed shed (P - r_up >= 0), down reserve is committed extra
consumption (P + r_down <= forecast). Dispatch limits move to the range
expressions only when a reserve service is attached, and a costless load
selling reserves fails loudly since nothing pins its consumption.

…-out

End-to-end market test: an elastic OnlineReserve (StepwiseCostReserve)
and a GroupStepwiseCostReserve group co-clear against per-resource
offers from thermal, storage, and load participants. Registers
GroupStepwiseCostReserve in the formulation library, refreshes the
stale group-reserve warnings there, and renames the remaining
market-specific reserve identifiers in hydro to generic ones.

Non-spinning is upward-only, so OfflineReserve routes like an up
reserve everywhere a device supplies it. New UP_RESERVE union in
reserve_traits.jl; storage reserve-balance multipliers, coverage
branches (two of which silently skipped OfflineReserve, one asserted),
get_fraction, and the TotalReserveOffering fold widened; load routing
and folding accept it as committed shed. The _modify_device_model!
no-op is scoped to NonSpinningReserve, whose awards ride
ReservePowerConstraint instead of the device range expressions.

PowerSystems psy6 (post schema-matching merge) depends on the
unregistered PowerCoreOpenAPIModels / PowerOperationsOpenAPIModels.
Pkg ignores [sources] of non-root projects, so each environment that
resolves PSY - root, test, docs - must pin them itself; CI failed with
'PowerOperationsOpenAPIModels has no known versions' on all jobs.
Pins mirror PSY's own (monorepo main, subdirs) and are temporary until
the packages are registered.

…supply

One demand curve on a PSY.GroupReserve is cleared by the summed awards of its
contributing services: a dense ServiceRequirementVariable per group, a clearing
constraint sum(member awards) >= demand variable (its dual is the group price),
and the group curve priced through the delta-PWL path. Static and time-series
group curves are both supported via the existing service-side TS machinery.

- Group demand predicates mirror the service formulations: GroupRangeReserve is
  driven by the scalar requirement, GroupStepwiseCostReserve by the demand curve;
  degenerate groups skip as supply aggregates with a warning.
- Group deferral generalized to a vector so up and down groups coexist.
- RESERVE_PRODUCT_TYPES (definitions.jl) consolidates the open
  Union{PSY.AbstractReserve, PSY.GroupReserve} signature bound used across the
  reserve traits, PWL parameter chain, and objective plumbing.
- Formulation-pairing guards: a GroupReserve accepts only group formulations and
  vice versa, failing with ArgumentError at ServiceModel declaration.
- Tests cover build/solve, aggregation binding, merit order, no-group baseline,
  the degenerate skip, TS group curves, and the pairing guards.

PSY moved GroupReserve into the reserve tree, so the RESERVE_PRODUCT_TYPES
alias and the per-type methods that existed only because groups sat outside
it are gone: every former Union bound is plain PSY.AbstractReserve, the
group get_initial_conditions_service_model and the CostExpressions container
sibling fold into the AbstractReserve methods, and uses_compact_power opens
to the abstract type. Formulation-pair bounds
(Union{StepwiseCostReserve, GroupStepwiseCostReserve}) and the group demand
predicates stay - they encode formulation semantics, not typing.

The pairing guards merge with the #235 hardening set: valid direction-applied
pairs for both group formulations, the generic-defaults disambiguator, the
inverse guard over both formulations, and a direction-required error for
bare GroupReserve declarations.

A controllable load routes reserves inversely to generators: up reserve
is committed shed (P - r_up >= 0), down reserve is committed extra
consumption (P + r_down <= forecast). Dispatch limits move to the range
expressions only when a reserve service is attached, and a costless load
selling reserves fails loudly since nothing pins its consumption.

…-out

End-to-end market test: an elastic OnlineReserve (StepwiseCostReserve)
and a GroupStepwiseCostReserve group co-clear against per-resource
offers from thermal, storage, and load participants. Registers
GroupStepwiseCostReserve in the formulation library, refreshes the
stale group-reserve warnings there, and renames the remaining
market-specific reserve identifiers in hydro to generic ones.

PowerSystems psy6 (post schema-matching merge) depends on the
unregistered PowerCoreOpenAPIModels / PowerOperationsOpenAPIModels.
Pkg ignores [sources] of non-root projects, so each environment that
resolves PSY - root, test, docs - must pin them itself; CI failed with
'PowerOperationsOpenAPIModels has no known versions' on all jobs.
Pins mirror PSY's own (monorepo main, subdirs) and are temporary until
the packages are registered.

…na/PowerOperationsModels.jl into rh/new_load_and_group_services