[5.x] Memoize matching shipping rule per method per request

[lukeholder]

Description

Performance improvements for stores with a large number of shipping rules.

• ShippingMethod::matchOrder() and getPriceForOrder() both previously walked all shipping rules independently. The matching rule is now cached on the method instance per order so the rule list is only walked once.
• Instead of loading all shipping rules into memory upfront, rules are now streamed from the database in batches of 200 during matching. Each rule is instantiated, tested, then discarded — peak memory is proportional to the batch size rather than the total number of rules.
• Disabled rules are filtered out in SQL rather than in PHP.