HPCC-12729 Redesign memcached plugin exception handling

Removed all WU exceptions -> rtlFails primarily via assertOnError.
reportErrorOnFail -> logErrorOnFail but is only used once (could remove) left for possible future use.
All others use ICodeContext::logString directly

All reports at least have some info about where they came from, i.e. no naked reports of memcached_return_t

Changed all 'servers' ids to 'options', likewise for 'error' -> 'rc'

Removed BOOLEAN return types from Set functions (and Clear) as they now fail on error.

Signed-off-by: James Noss <james.noss@lexisnexis.com>