fix(azure): hoursPerMonth is 730.5 while docs and SP terms assume 730/8760 #583

Found while reviewing #582 (part of #109).

providers/azure defines hoursPerMonth = DaysPerMonth*24 = 730.5 (benefit_recommendations.go:49, with DaysPerMonth = 30.4375). But that file's own doc (~:245-246) says 730, pkg/common.HoursPerMonth is 730, and Azure Savings Plan terms use 8760 hours a year (savingsplans/client.go:586). 730.5 × 12 = 8766, so monthly and annual figures for the same commitment disagree by about 0.07%.

Decide which definition is correct for Azure benefit recommendations (Azure's own pricing pages use 730 hours a month), make the code and docs consistent, and use common.HoursPerMonth if 730 is right. Add a test pinning the value.