The buildSearchFilter function doesn't need to be exported, and
can use strings.Builder. Add a unit test to make sure this didn't
change any logic.
This will also use the debuglogger to enable debugging.
The debuglogger should be a top level module since we expect
all modules within the project to make use of this. If its
hidden in s3api, then contributors are less likely to make
use of this outside of s3api.