fix: enable clear time keymap consistently

To be able to clear times if no timestamp was set when the picker was
loaded, we need to set the clear-time keymapping during rerendering of
time.

lua/orgmode/objects/calendar.lua

@@ -135,6 +135,7 @@ function Calendar:open()
     self:set_time()
   end, map_opts)
   if self:has_time() then
+    print('apply clear_time')
     vim.keymap.set('n', 'T', function()
       self:clear_time()
     end, map_opts)
@@ -579,6 +580,9 @@ function Calendar:rerender_time()
   vim.api.nvim_set_option_value('modifiable', true, { buf = self.buf })
   vim.api.nvim_buf_set_lines(self.buf, 8, 9, true, { self:render_time() })
   if self:has_time() then
+    vim.keymap.set('n', 'T', function()
+      self:clear_time()
+    end, { buffer = self.buf, silent = true, nowait = true })
     vim.api.nvim_buf_set_lines(self.buf, 13, 14, true, { ' [t] - enter time  [T] - clear time' })
     vim.api.nvim_buf_add_highlight(self.buf, namespace, 'Normal', 8, 0, -1)
     vim.api.nvim_buf_add_highlight(self.buf, namespace, 'Comment', 13, 0, -1)