chore: update code.highlight_border to false|string instead of boolean|string

## Details

Setting `code.highlight_border` to `true` really makes no sense, since
the point is to disable border highlighting, which means the same things
as disabling the border. Update the type definition and usage to only
allow for `false` rather than handling `true` in the same way.

Author: MeanderingProgrammer

doc/render-markdown.txt

@@ -1,4 +1,4 @@
-*render-markdown.txt*        For NVIM v0.11.2        Last change: 2025 June 11
+*render-markdown.txt*        For NVIM v0.11.2        Last change: 2025 June 12
 
 ==============================================================================
 Table of Contents                          *render-markdown-table-of-contents*

lua/render-markdown/config/code.lua

@@ -19,7 +19,7 @@
 ---@field inline_pad integer
 ---@field highlight string
 ---@field highlight_language? string
----@field highlight_border string|boolean
+---@field highlight_border false|string
 ---@field highlight_fallback string
 ---@field highlight_inline string
 
@@ -151,7 +151,7 @@ function M.validate(spec)
     spec:type('inline_pad', 'number')
     spec:type('highlight', 'string')
     spec:type('highlight_language', { 'string', 'nil' })
-    spec:type('highlight_border', { 'string', 'boolean' })
+    spec:one_of('highlight_border', { false }, 'string')
     spec:type('highlight_fallback', 'string')
     spec:type('highlight_inline', 'string')
     spec:check()

lua/render-markdown/debug/validator.lua

@@ -72,7 +72,7 @@ function Spec:type(keys, ts)
 end
 
 ---@param keys string|string[]
----@param values string[]
+---@param values any[]
 ---@param ts? type|type[]
 function Spec:one_of(keys, values, ts)
     local options = Iter.list.map(values, vim.inspect)
@@ -138,7 +138,7 @@ function Spec:nested_list(keys, t, ts)
 end
 
 ---@param keys string|string[]
----@param values string[]
+---@param values any[]
 ---@param ts? type|type[]
 function Spec:one_or_list_of(keys, values, ts)
     local body = table.concat(Iter.list.map(values, vim.inspect), '|')
@@ -147,17 +147,15 @@ function Spec:one_or_list_of(keys, values, ts)
     self:add(keys, Kind.type, message, function(value)
         if vim.tbl_contains(types, type(value)) then
             return true
-        elseif type(value) == 'string' then
+        elseif type(value) ~= 'table' then
             return vim.tbl_contains(values, value)
-        elseif type(value) == 'table' then
+        else
             for i, item in ipairs(value) do
                 if not vim.tbl_contains(values, item) then
                     return false, ('[%d] is %s'):format(i, item)
                 end
             end
             return true
-        else
-            return false
         end
     end)
 end

lua/render-markdown/health.lua

@@ -5,7 +5,7 @@ local state = require('render-markdown.state')
 local M = {}
 
 ---@private
-M.version = '8.5.1'
+M.version = '8.5.2'
 
 function M.check()
     M.start('version')

lua/render-markdown/render/markdown/code.lua

@@ -122,11 +122,11 @@ function Render:language(language, delim)
         return false
     end
 
-    local highlight = {}
+    local highlight = {} ---@type string[]
     local fallback_highlight = self.config.highlight_fallback
     highlight[#highlight + 1] = (icon_highlight or fallback_highlight)
     local border_highlight = self.config.highlight_border
-    if type(border_highlight) == 'string' then
+    if border_highlight ~= false then
         highlight[#highlight + 1] = border_highlight
     end
 
@@ -163,7 +163,7 @@ end
 function Render:border(node, icon, empty)
     local kind = self.config.border
     local highlight = self.config.highlight_border
-    if not node or kind == 'none' or type(highlight) == 'boolean' then
+    if not node or kind == 'none' or highlight == false then
         return
     end
     local row = node.start_row

lua/render-markdown/types.lua

@@ -102,7 +102,7 @@
 ---@field inline_pad? integer
 ---@field highlight? string
 ---@field highlight_language? string
----@field highlight_border? string|boolean
+---@field highlight_border? false|string
 ---@field highlight_fallback? string
 ---@field highlight_inline? string