[ADD] website_sale_product_attribute_filter_range: range slider filter for numeric attributes

[munikes]

Summary

• Adds a new Range Slider display type for product attributes on the website shop
• When configured, the attribute appears as a dual-handle range slider (similar to the built-in price filter) instead of standard checkboxes
• Allows customers to filter products by numeric ranges (scores, weights, dimensions, etc.)

Features

• New "Range Slider" option in attribute Display Type (selection_add)
• Configurable Range Step increment per attribute
• Automatic Numeric Value parsing from attribute value names (supports dot and comma decimals)
• Works in both desktop sidebar and mobile offcanvas
• SQL constraint ensures range attributes use no_variant mode
• URL parameter format: attrib_range=attr_id-min-max

Configuration

1. Go to Inventory > Configuration > Attributes
2. Set Display Type to Range Slider
3. Set the Range Step (default 0.5)
4. Ensure attribute values have the Numeric Value field set

Test plan

• 5 unit tests passing on Odoo 18.0 (Odoo.sh)
• Desktop sidebar: slider in correct position
• Mobile offcanvas: slider between attributes and price filter
• URL filtering works (?attrib_range=9-82-88)
• Constraint prevents range + variant creation
• i18n: Spanish translations included