3x slowdown in DebugOptimized kv_engine test runtime with jemalloc debug library

As part of MB-51532, the debug variant of jemalloc (libjemallocd.so) was used for debug build types - "Debug" and "DebugOptimized". This has resulted in a significant increase in the runtime of CV tests - for example on macOS (Apple M1 Pro), DebugOptimized build the total runtime for all kv_engine tests is now:

Total Test time (real) = 518.24 sec

real	8m38.260s

user	61m50.453s

sys	3m2.256s

Compared to before when DebugOptimized used the non-debug variant of jemalloc ( https://review.couchbase.org/c/tlm/+/172964 ):

Total Test time (real) = 177.53 sec

real    2m57.544s

user    16m30.490s

sys 2m44.285s

i.e user+sys has increased from 19m14s to 64m42s - over 3x slower.

While enabling extra debug checks for DebugOptimized can be useful, having it cost 3x in test runtime is not really an acceptable trade-off.