fix(lsp): scope inline_completion autocmds to buffer (#35965)

Problem:
Autocmds in inline_completion Completor are not scoped to specific
buffers. When multiple buffers have inline completion enabled, events
(InsertEnter, CursorMovedI, TextChangedP, InsertLeave) in any buffer
trigger callbacks for all Completor instances, causing incorrect
behavior across buffers.

Solution:
Add `buffer = bufnr` parameter to nvim_create_autocmd() calls to make
them buffer-local. Each Completor instance now only responds to events
in its own buffer.

runtime/lua/vim/lsp/inline_completion.lua

@@ -76,12 +76,14 @@ function Completor:new(bufnr)
   self.client_state = {}
   api.nvim_create_autocmd({ 'InsertEnter', 'CursorMovedI', 'TextChangedP' }, {
     group = self.augroup,
+    buffer = bufnr,
     callback = function()
       self:automatic_request()
     end,
   })
   api.nvim_create_autocmd({ 'InsertLeave' }, {
     group = self.augroup,
+    buffer = bufnr,
     callback = function()
       self:abort()
     end,