fix: schedule initial buffer attach to handle lazy loading edge cases

## Details

Issue: #315

Previously we added a step to attach to the current buffer to handle
`vim-plug` based lazy loading not running for the initial file.

This causes a problem with `lazy.nvim` since the attach function will
run before picking up user configuration values, which will cause the
first buffer to be out of sync from the user configuration.

As a sort of hacky but good enough solution run the lazy load handling
attach calls behind a vim.schedule. This should result in the event
based ones running first and avoid this problem.

Author: MeanderingProgrammer

Diff for: doc/render-markdown.txt

@@ -1,4 +1,4 @@
-*render-markdown.txt*          For 0.10.0         Last change: 2025 January 28
+*render-markdown.txt*          For 0.10.0         Last change: 2025 January 31
 
 ==============================================================================
 Table of Contents                          *render-markdown-table-of-contents*

Diff for: lua/render-markdown/health.lua

@@ -5,7 +5,7 @@ local state = require('render-markdown.state')
 local M = {}
 
 ---@private
-M.version = '7.8.12'
+M.version = '7.8.13'
 
 function M.check()
     M.start('version')

Diff for: lua/render-markdown/manager.lua

@@ -15,7 +15,7 @@ M.group = vim.api.nvim_create_augroup('RenderMarkdown', { clear = true })
 ---Should only be called from plugin directory
 function M.setup()
     -- Lazy Loading: ignores current buffer as FileType event already executed
-    M.attach(util.current('buf'))
+    M.schedule_attach()
     -- Attempt to attach to all buffers, cannot use pattern to support plugin directory
     vim.api.nvim_create_autocmd('FileType', {
         group = M.group,
@@ -43,7 +43,7 @@ end
 ---@param enabled boolean
 function M.set_all(enabled)
     -- Lazy Loading: all previously opened buffers have been ignored
-    M.attach(util.current('buf'))
+    M.schedule_attach()
     state.enabled = enabled
     for _, buf in ipairs(buffers) do
         ui.update(buf, vim.fn.bufwinid(buf), 'UserCommand', true)
@@ -56,6 +56,14 @@ function M.is_attached(buf)
     return vim.tbl_contains(buffers, buf)
 end
 
+---@private
+function M.schedule_attach()
+    local buf = util.current('buf')
+    vim.schedule(function()
+        M.attach(buf)
+    end)
+end
+
 ---@private
 ---@param buf integer
 function M.attach(buf)