Open blocker-level tickets for any blocker-level TODO HS items.

Currently there are TODO HS items in these crates:

• arti-client
• tor-cert (also see !1311 (merged))
• tor-circmgr
• tor-dirclient
• tor-hsclient (@Diziet, #931 (closed))
• tor-keymgr (@gabi-250 #933 (closed))
• tor-netdir (partially done in !1310 (merged))
• tor-netdoc (see !1309 (closed))
• tor-proto (also see #917 (closed))

We should confirm, for each crate, whether any of the TODO HS items is a release Blocker. We should check off those crates when we have opened tickets for every such Blocker, or confirmed that there are none.