Feat/retire fallback scheduler

[BelhsanHmida]

Description

• Turn on SoC constraint relaxation by default for storage scheduling requests.
• Remove the built-in storage fallback scheduler, so infeasible storage problems now surface as scheduling failures instead of silently producing fallback schedules.
• Keep the generic fallback redirect/job machinery available for custom schedulers.
• Update tests and documentation to reflect the new default relaxation and infeasibility behavior.
• Changelog entry added

Look & Feel

N/A

How to test

pytest flexmeasures/data/schemas/tests/test_scheduling.py \
  flexmeasures/api/v3_0/tests/test_sensor_schedules.py \
  flexmeasures/data/tests/test_scheduling_sequential.py \
  flexmeasures/data/models/planning/tests/test_storage.py

Also ran the targeted solver fallback-retirement test.

Related Items

Closes #2201

Sign-off

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• I certify that I wrote the contribution or otherwise have the right to submit it under the project license.

[BelhsanHmida]

Manual test done through Swagger UI:

1. Triggered a storage schedule through:

POST /api/v3_0/assets/8/schedules/trigger

with a flex model that creates a failing storage scheduling job.

2. The trigger request was accepted and returned a schedule job UUID:

775b2af5-88dd-4988-affd-8b11ec025841

3. Fetched the schedule through:

GET /api/v3_0/sensors/23/schedules/775b2af5-88dd-4988-affd-8b11ec025841?duration=PT24H&unit=kW&sign-convention=consumption-positive

4. The response was:

400 BAD REQUEST

with:

{
  "message": "No known schedule for this time period. Scheduling job failed with ValueError: Power capacity on asset 8 is not defined in the flex-model. StorageScheduler was used.",
  "result": "Rejected",
  "status": "UNKNOWN_SCHEDULE"
}