Prepare for release 3.8.0

[cboulay]

Includes the following merged PRs:

• hot fix 217 - recalculate Subscriber's pub keys on demand by @cboulay in hot fix 217 - recalculate Subscriber's pub keys on demand #218
• Deprecate zero-copy keyword argument in @ez.subscriber by @griffinmilsap in Deprecate zero-copy keyword argument in @ez.subscriber #216
• Wrap shutdown_units().result() and context.revert().result() with whi… by @cboulay in Wrap shutdown_units().result() and context.revert().result() with whi… #221
• Fix: Multiple shutdown issues and enhance shutdown UX by @cboulay in Fix: Multiple shutdown issues and enhance shutdown UX #220
• Feature: Synchronous Low‑Level API for ezmsg (ROS2‑style ergonomics) by @griffinmilsap in Feature: Synchronous Low‑Level API for ezmsg (ROS2‑style ergonomics) #215
• Dev --> Main by @griffinmilsap in Dev --> Main #222