Net::CmdStreamer: updated commit_direct() calls.¹

1: For duct::IO::dynamic_streambuf. Recent duct++ change made read
position retention an explicit request/reset.
Net::CmdStreamer: updated use of Context and Cmd::type_info.
Client::Unit: updated m_driver initialization.¹

1: Not far enough ahead to know if I want stuff like slug-path maps
in the Hive or not (as runtime data), so using the standard type
registration for now.
IO::FlatDatastore: removed Index; updated for Datastore changes; misc tweaks & tidy.

IO::FlatDatastore:
	changed hive file structure according to linkage;
	added a static_assert() to ensure the ID sprintf() in assign_prop() fits;
	corrected assign_prop() pathing (was missing slash after prop abbr);
	error tidy;
	tidy.