[receiver/snowflake] Fix storage metric reporting bug

[shalper2]

Description: Identified and fixed an issue with the function responsible for querying storage metrics in client.go. The issue was that sql.Rows.Scan() was receiving a float64 instead of an int64 as previously thought and so trying to copy the column values into the provided variable pointers was causing a type error. To fix this the type of the variables passed into sql.Rows.Scan() was changed to float64 and then recast as int64 when inserting into the metric interface. This made more sense than potentially breaking existing pipelines by changing the metric type to double especially since the values for these metrics is always an integer (even if the database itself stores them as a float).

Link to tracking Issue: 29750

Testing: Modified tests to expect float values from the mock database

Documentation: No change needed