feat: add after render callback

## Details

Request: #248

Adds `on.render` callback which is executed after this plugin finishes
rendering a buffer.

This happens after every render cycle, users should be aware that it
will likely be called many times for a given buffer and use it with that
in mind.

Author: MeanderingProgrammer

README.md

@@ -207,6 +207,8 @@ require('render-markdown').setup({
     on = {
         -- Called when plugin initially attaches to a buffer
         attach = function() end,
+        -- Called after plugin renders a buffer
+        render = function() end,
     },
     heading = {
         -- Turn on / off heading icon & background rendering

doc/render-markdown.txt

@@ -1,4 +1,4 @@
-*render-markdown.txt*         For 0.10.0         Last change: 2024 December 05
+*render-markdown.txt*         For 0.10.0         Last change: 2024 December 06
 
 ==============================================================================
 Table of Contents                          *render-markdown-table-of-contents*
@@ -254,6 +254,8 @@ Default Configuration ~
         on = {
             -- Called when plugin initially attaches to a buffer
             attach = function() end,
+            -- Called after plugin renders a buffer
+            render = function() end,
         },
         heading = {
             -- Turn on / off heading icon & background rendering

lua/render-markdown/core/ui.lua

@@ -134,6 +134,7 @@ function M.run_update(buf, win, parse)
                 extmark:show(M.namespace, buf)
             end
         end
+        state.on.render(buf)
     else
         M.clear(buf, buffer_state)
     end

lua/render-markdown/health.lua

@@ -4,7 +4,7 @@ local state = require('render-markdown.state')
 local M = {}
 
 ---@private
-M.version = '7.6.11'
+M.version = '7.6.12'
 
 function M.check()
     M.start('version')

lua/render-markdown/init.lua

@@ -13,6 +13,7 @@ local M = {}
 
 ---@class (exact) render.md.UserCallback
 ---@field public attach? fun(buf: integer)
+---@field public render? fun(buf: integer)
 
 ---@class (exact) render.md.UserLatex
 ---@field public enabled? boolean
@@ -341,6 +342,8 @@ M.default_config = {
     on = {
         -- Called when plugin initially attaches to a buffer
         attach = function() end,
+        -- Called after plugin renders a buffer
+        render = function() end,
     },
     heading = {
         -- Turn on / off heading icon & background rendering

lua/render-markdown/state.lua

@@ -307,7 +307,7 @@ function M.validate()
                 :check()
         end)
         :nested('on', function(on)
-            on:type('attach', 'function'):check()
+            on:type({ 'attach', 'render' }, 'function'):check()
         end)
         :nested('overrides', function(overrides)
             overrides

lua/render-markdown/types.lua

@@ -2,6 +2,7 @@
 
 ---@class (exact) render.md.Callback
 ---@field public attach fun(buf: integer)
+---@field public render fun(buf: integer)
 
 ---@class (exact) render.md.Latex
 ---@field public enabled boolean