Add feed only simulation type

[matthew7838]

Adds a feed_only simulation type so the Feed Storage module can run on its own.

Context

Issue(s) closed by this pull request: closes #2988

What

• New SimulationType.FEED_ONLY ("feed_only") and its daily routine.
• New optional input: initial feed storage contents, keyed by storage instance name.
• Storage.stock_initial_contents() and FeedManager.stock_initial_storage_contents().
• Extracted SimulationEngine._execute_feed_storage_upkeep() out of _execute_feed_planning().
• New feed_only example scenario, registered in available_simulation_tasks.json.

Why

• Feed storages only fill from field harvests, so without the crop and soil module they stay empty for the whole run.
• Storage contents have to come from somewhere: this states them as an initial condition instead of inventing harvests.
• Feed planning is gated on a harvest schedule, so degradations would never run in a simulation with no harvests.

How

• Initial contents are stocked once at setup, through Storage.receive_crop, so capacity checks and grain / high moisture arrival losses still apply.
• Daily routine is storage upkeep (report levels, process degradations) then record keeping.
• Feed planning is not called: with no animals, ideal_feeds_to_purchase is always empty, so the purchasing path is a no-op.
• Stocking runs for every feed simulating type and is opt-in by input presence, so existing scenarios are unaffected.

Test plan

• 7109 unit tests pass. New tests for Storage.stock_initial_contents, FeedManager.stock_initial_storage_contents, _gather_initial_feed_storage_contents, and the feed only daily routine.
• All 4 e2e scenarios pass every domain, confirming the upkeep extraction changed no existing output.
• All 6 example scenarios run with 0 errors, including the new feed_only.
• 7 year feed_only run: 445,000 kg DM stocked, 322,684 kg DM remaining (27.5% loss; alfalfa silage 51.6%, corn silage 30.8%, hay 17.7%, dry grain 1.0%).

Input Changes

• Added input/data/feed_management/example_feed_only_initial_contents.json.
• Added input/data/config/example_feed_only_config.json, input/metadata/example_feed_only_metadata.json, input/data/tasks/example_feed_only_task.json.
• Added initial_feed_storage_contents_properties and feed_only to the simulation_type pattern in default.json.
• Added a feed_only entry to available_simulation_tasks.json.

Output Changes

• N/A for existing simulation types. The new feed_only scenario reports existing feed storage variables only.

Filter

Notes for reviewers

• Only the storage half of the module runs: with no animals and no purchases, FeedManager's feeding, purchasing, and inventory projection paths are never reached. Measured feed module coverage in a feed_only run is 67% (storage.py 87%, silage.py 87%, hay.py 87%, feed_manager.py 37%). Whether that is enough for "FeedManager only" is worth a look before merge.
• Optional inputs have to be separate metadata blobs. An optional nested object inside the existing storage configs fails validation, since objects are not fixable and cannot be nullable.

[github-actions]

Current Coverage: %

Mypy errors on feed-only-simulation-2988 branch: 1139
Mypy errors on dev branch: 1135
4 more errors on feed-only-simulation-2988 branch

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🚨 Some tests have failed.

[github-actions]

Current Coverage: 99%

Mypy errors on feed-only-simulation-2988 branch: 1139
Mypy errors on dev branch: 1135
4 more errors on feed-only-simulation-2988 branch

[github-actions]

Current Coverage: 99%

Mypy errors on feed-only-simulation-2988 branch: 1139
Mypy errors on dev branch: 1135
4 more errors on feed-only-simulation-2988 branch