API getusers/getgroups performance optimization

With my test data (a few hundred users, uffd_access containing all, uffd_admin only a few) I got:

master

• getusers -> 0m02.06s/0m01.19s/0m01.22s
• getusers?group=uffd_access -> 0m01.16s/0m01.09s/0m01.23s
• getusers?group=uffd_admin -> 0m00.65s/0m00.85s/0m00.86s
• getusers?loginname=testadmin -> 0m00.28s/0m00.24s/0m00.20s
• getusers?id=10649 -> 0m00.22s/0m00.28s/0m00.29s
• getgroups -> 0m00.80s/0m00.89s/0m00.82s
• getgroups?name=uffd_access -> 0m00.05s/0m00.05s/0m00.03s
• getgroups?name=uffd_admin -> 0m00.02s/0m00.02s/0m00.02s

api-performance

• getusers -> 0m00.54s/0m00.52s/0m00.53s
• getusers?group=uffd_access -> 0m00.49s/0m00.44s/0m00.53s
• getusers?group=uffd_admin -> 0m00.09s/0m00.09s/0m00.08s
• getusers?loginname=testadmin -> 0m00.02s/0m00.02s/0m00.02s
• getusers?id=10649 -> 0m00.03s/0m00.03s/0m00.03s
• getgroups -> 0m00.39s/0m00.51s/0m00.58s
• getgroups?name=uffd_access -> 0m00.04s/0m00.03s/0m00.05s
• getgroups?name=uffd_admin -> 0m00.02s/0m00.02s/0m00.03s