Add output history replay

[bigfactory]

Summary

• Add an in-memory ring buffer for recent program output in the master process.
• Replay retained output history when a new client attaches.
• Add -H <bytes> to configure history size, with -H 0 disabling replay.
• Document the new option in the man page and help output.

Test Plan

• make -C /Users/bytedance/Github/dtach
• Verified default history replay by starting an unattached session that prints output, then attaching and checking the output is replayed.
• Verified -H 0 disables history replay.
• Verified small history buffers keep only the newest bytes.
• Verified invalid -H values are rejected.

[rdebath]

There is another class of controls you will want to filter, the persistent state controls. Probably the common ones are the 'alternate screen' selection and the mouse control. The thing is you don't want to remove them, you want to hold the last state seen before the beginning of the buffer.

Unfortunately, it would also be nice to reset those when detaching; which would mean a lot more proactive understanding.
Like lists of ECMA-48 sequences with the first of each set being the reset.

Also CSI c CSI >c CSI ? 15n \033[?1049$p and loads more from XTerm, old XTerm, real VTs and others.