fix(tui): attribute TermResponse to source channel #40330

Problem: Attach-time terminal probes cannot distinguish responses from
different attached UIs.

Solution: Identify the UI by RPC channel id in `TermResponse` and make
`vim.tty.request()` filter responses by channel.

runtime/lua/vim/_meta/events.lua

@@ -60,4 +60,5 @@ error('Cannot require a meta file')
 --- @field cursor integer[]
 
 --- @class vim.event.termresponse.data
+--- @field chan integer
 --- @field sequence string