feat(net): vim.net.request(), :edit [url] #34140

Problem:
Nvim depends on netrw to download/request URL contents.

Solution:
- Add `vim.net.request()` as a thin curl wrapper:
  - Basic GET with --silent, --show-error, --fail, --location, --retry
  - Optional `opts.outpath` to save to a file
  - Operates asynchronously. Pass an `on_response` handler to get the result.
- Add integ tests (requires NVIM_TEST_INTEG to be set) to test success
  and 404 failure.
- Health check for missing `curl`.
- Handle `:edit https://…` using `vim.net.request()`.

API Usage:
1. Asynchronous request:

    vim.net.request('https://httpbingo.org/get', { retry = 2 }, function(err, response)
      if err then
        print('Fetch failed:', err)
      else
        print('Got body of length:', #response.body)
      end
    end)

2. Download to file:

    vim.net.request('https://httpbingo.org/get', { outpath = 'out_async.txt' }, function(err)
      if err then print('Error:', err) end
    end)

3. Remote :edit integration (in runtime/plugin/net.lua) fetches into buffer:

    :edit https://httpbingo.org/get

runtime/plugin/nvim/net.lua

@@ -0,0 +1,43 @@
+vim.g.loaded_remote_file_loader = true
+
+--- Callback for BufReadCmd on remote URLs.
+--- @param args { buf: integer }
+local function on_remote_read(args)
+  if vim.fn.executable('curl') ~= 1 then
+    vim.api.nvim_echo({
+      { 'Warning: `curl` not found; remote URL loading disabled.', 'WarningMsg' },
+    }, true, {})
+    return true
+  end
+
+  local bufnr = args.buf
+  local url = vim.api.nvim_buf_get_name(bufnr)
+  local view = vim.fn.winsaveview()
+
+  vim.api.nvim_echo({ { 'Fetching ' .. url .. ' …', 'MoreMsg' } }, true, {})
+
+  vim.net.request(
+    url,
+    { retry = 3 },
+    vim.schedule_wrap(function(err, content)
+      if err then
+        vim.notify('Failed to fetch ' .. url .. ': ' .. tostring(err), vim.log.levels.ERROR)
+        vim.fn.winrestview(view)
+        return
+      end
+
+      local lines = vim.split(content.body, '\n', { plain = true })
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, true, lines)
+
+      vim.fn.winrestview(view)
+      vim.api.nvim_echo({ { 'Loaded ' .. url, 'Normal' } }, true, {})
+    end)
+  )
+end
+
+vim.api.nvim_create_autocmd('BufReadCmd', {
+  group = vim.api.nvim_create_augroup('nvim.net.remotefile', {}),
+  pattern = { 'http://*', 'https://*' },
+  desc = 'Edit remote files (:edit https://example.com)',
+  callback = on_remote_read,
+})