Wrap field in <pre> tags

There may be contrib modules to do that, but a very simple way to do this is to override the field template, and putting that file in your themes/MY_THEME/templates folder.

For example, to override the body field template, you should put your code in a file called field--body.tpl.php and place it in core/theme/basis/templates, or if you are using another theme, in themes/MY_THEME/templates.

You can see an example of the default code that Backdrop uses to theme fields by looking at core/modules/field/templates/field.tpl.php, (also here) but please notice that THAT particular template is not used - it's there as an example to help you override the field templates.

Also, take a look at the different patterns you can use to override fields in specific content types by looking at this help text. 

The Field Wrappers module is very easy to extend to add the wrappers you need. There is an example in the wiki and in the API.php file in the module.