Add support for synchronized output to prevent tearing

If I run an application which continuously sends large chunks of text + ANSI control sequences to stdout, I sometimes see the cursor jump to the middle of the rendering. The application is enabling mode 2026 and sending the end-of-frame sequences. VHS should track whether this mode is enabled and not re-render a frame until it sees the end-of-frame sequence.

More details available at https://gist.github.com/christianparpart/d8a62cc1ab659194337d73e399004036

Start by tracing VHS's terminal rendering and ANSI control-sequence handling, then read the linked gist for the synchronized-output protocol. The change is complete when mode 2026 is tracked and frames are not re-rendered until the end-of-frame sequence is received; verify this with a continuously writing application that emits large text chunks.

Written by the indexing model from the issue text.