Mining computation update

* Added various views and helper functions used by the mining
computation but which may be re-used in other parts.

* Added mining computation update type and associated update function

* New constants: game.resources.weightBase (the value used to compute
weights from mining settings) and game.resources.extraction (the
quantity extracted in a day from a full provider at difficulty 0)

legacyworlds-server-data/db-structure/parts/030-data/000-typedefs.sql

@@ -83,7 +83,10 @@ CREATE TYPE update_type	AS ENUM (
 	'PLANET_RES_REGEN' ,
 
 	/* Compute income and upkeep of planets */
-	'PLANET_MONEY'
+	'PLANET_MONEY' ,
+	
+	/* Compute mining results for planets owned by empires */
+	'PLANET_MINING'
 );
 
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