# POS Attribute Image Lazy Loading

Keeps `product.attribute.value` images out of the `pos.session.load_pos_data`
payload.

## The problem

`pos.session._get_attributes_by_ptal_id()` inlines the base64 `image` of every
attribute value of a `create_variant='no_variant'` attribute, **once per
attribute line** referencing it. With a handful of photo sized images this grows
without bound and the request dies while serialising the response:

```
File "werkzeug/wrappers/response.py", line 327, in set_data
    value = value.encode(self.charset)
MemoryError
```

The browser only sees `ConnectionLostError` on
`/web/dataset/call_kw/pos.session/load_pos_data`, with no traceback in the POS.

Note that `product.attribute.value.image` is capped at 70x70 upstream, but
`product.template.attribute.value.image` is a related field declared without
`max_width`/`max_height`, so uploading through a product template's attribute
lines stores the original untouched.

## The fix

The POS front end never reads those bytes. `point_of_sale.ColorProductAttribute`
only tests the field for truthiness and renders the swatch from
`/web/image/product.template.attribute.value/<id>/image`. Reading under
`bin_size` returns the attachment size instead of its content, which is still
truthy, so nothing changes visually.

Measured on a production database with 224 images of ~1 MB:

| | `load_pos_data` payload |
|---|---|
| Without the module | 145.93 MB |
| With the module | 0.51 MB |