fix: ignore inline highlights that start or end in nested node

## Details

Issue: #568

Since inline highlights are not actually part of the parser they are
calculated by finding text inside `==`. This means it picks up text that
starts / ends in code spans, emphasis blocks, and all other kinds of
nested inline nodes. As a simple fix for this we now check that the
start and end are at the top level, meaning the node type is `inline`.

Author: MeanderingProgrammer

doc/render-markdown.txt

@@ -1,4 +1,4 @@
-*render-markdown.txt*      For NVIM v0.11.5      Last change: 2025 December 11
+*render-markdown.txt*      For NVIM v0.11.5      Last change: 2025 December 14
 
 ==============================================================================
 Table of Contents                          *render-markdown-table-of-contents*

lua/render-markdown/health.lua

@@ -6,7 +6,7 @@ local state = require('render-markdown.state')
 local M = {}
 
 ---@private
-M.version = '8.10.7'
+M.version = '8.10.8'
 
 function M.check()
     M.start('versions')

lua/render-markdown/render/inline/highlight.lua

@@ -18,28 +18,45 @@ end
 ---@protected
 function Render:run()
     for _, range in ipairs(self.node:find('==[^=]+==')) do
-        -- hide first 2 equal signs
-        self:hide(range[1], range[2], range[2] + 2)
-        -- hide last 2 equal signs
-        self:hide(range[3], range[4] - 2, range[4])
+        local top_level = self:top_level(range[1], range[2])
+            and self:top_level(range[3], range[4])
+        if top_level then
+            -- hide first 2 equal signs
+            self:hide(range[1], range[2], range[2] + 2)
+            -- hide last 2 equal signs
+            self:hide(range[3], range[4] - 2, range[4])
 
-        local custom = self:custom(range, { 0, 2, 0, -2 })
-        local highlight = self.config.highlight
-        if custom then
-            -- hide custom prefix
-            self:hide(range[1], range[2] + 2, range[2] + 2 + #custom.prefix)
-            highlight = custom.highlight
-        end
+            local custom = self:custom(range, { 0, 2, 0, -2 })
+            local highlight = self.config.highlight
+            if custom then
+                -- hide custom prefix
+                self:hide(range[1], range[2] + 2, range[2] + 2 + #custom.prefix)
+                highlight = custom.highlight
+            end
 
-        -- highlight contents
-        self.marks:add(self.config, false, range[1], range[2], {
-            end_row = range[3],
-            end_col = range[4],
-            hl_group = highlight,
-        })
+            -- highlight contents
+            self.marks:add(self.config, false, range[1], range[2], {
+                end_row = range[3],
+                end_col = range[4],
+                hl_group = highlight,
+            })
+        end
     end
 end
 
+---@private
+---@param row integer
+---@param col integer
+---@return boolean
+function Render:top_level(row, col)
+    local node = vim.treesitter.get_node({
+        bufnr = self.context.buf,
+        pos = { row, col },
+        ignore_injections = false,
+    })
+    return node and node:type() == 'inline' or false
+end
+
 ---@private
 ---@param row integer
 ---@param start_col integer