Migrate most main_service.cc command handlers from CmdArgList to
CmdArgParser, following the same pattern as the recent set_family.cc
and zset_family.cc migrations.

- Update Quit, Multi, Watch, Unwatch, Discard, Exec, Publish,
  Subscribe, Unsubscribe, PSubscribe, PUnsubscribe, Function,
  Monitor, Pubsub, Command handlers
- Propagate ParsedArgs through ChangeSubscription/ChangePSubscription
  in conn_context.h/.cc to avoid CmdArgList conversion
- Update MFUNC macro to call MakeParserFromContext instead of
  passing CmdArgList; keep MFUNC_OLD for Eval* handlers (deferred)

Signed-off-by: Roman Gershman <roman@dragonflydb.io>