[Econ] HomeGrownFeed Revenue and Cost Processing

[allisterakun]

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Issue(s) closed by this pull request: closes #3079

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[allisterakun]

Resolved the missing commodity-price data for homegrown feeds using the mapping agreed in the email thread with the economics SMEs (Kristan Reed / Braden Limb).

Added HOMEGROWN_FEED_PRICE_ALIASES in mapping.py — feed crops without a dedicated commodity_prices_*_dollar_per_kilogram series now fall back to the closest available proxy commodity:

Feed crop	Proxy commodity
cereal_rye_grain, triticale_grain	rye_grain
cereal_rye_silage, cereal_rye_baleage, triticale_silage, triticale_baleage, winter_wheat_silage, winter_wheat_baleage	barley_silage
tall_fescue_silage, tall_fescue_baleage	sundan_silage
alfalfa_baleage	alfalfa_silage
cereal_rye_hay, triticale_hay, tall_fescue_hay, winter_wheat_hay	hay_excluding_alfalfa

On hay: per Braden, all_hay is inclusive of alfalfa while hay_excluding_alfalfa is all_hay minus the alfalfa data (per USDA, "various grass hays and other forage crops"). All non-alfalfa hay feeds are therefore mapped to hay_excluding_alfalfa for best price/cost accuracy.

_build_feed_id_to_price_file_map now resolves via _resolve_price_file_key, which prefers an exact match and otherwise applies the alias, emitting a MissingHomegrownFeedPriceMapping warning only when neither resolves. Added unit tests covering direct match, alias resolution, unmapped crops, the no-metadata path, and that every alias target resolves.