Improve speed of VerifySpAttributesConcern

[mitchellhenke]

Currently, VerifySpAttributesConcern makes repeated calls to sp_session_identity. The database call is cached after the first call, but there is still a noticeable amount of overhead in doing that.

This PR cleans up the behavior to only maybe hit the database once and passes the result to the functions that follow.

Performance benchmark available in commit b924b5a

# Warming up --------------------------------------
#             no cache     8.000  i/100ms
#                cache    50.000  i/100ms
# Calculating -------------------------------------
#             no cache     79.407  (±12.6%) i/s -      2.328k in  30.055220s
#                cache    449.444  (±10.9%) i/s -     13.300k in  30.030989s

# Comparison:
#                cache:      449.4 i/s
#             no cache:       79.4 i/s - 5.66x  (± 0.00) slower

[zachmargolis]

LGTM, another good find!