This commit introduces a new `merge` attribute to the `<attribute>` tag, allowing developers to safely merge existing dictionary-based or list-based attributes in XML view inheritance.

Problem:
Currently, when a developer needs to extend an attribute like `options` or `domain` in an inherited view, they must completely redefine the attribute, which can lead to unintended overwrites of properties set in the base view. For example, to add a new option, one must copy all existing options, which is tedious and brittle.

Solution:
The new `merge` attribute provides a declarative way to extend these attributes. When specified on an `<attribute>` tag, it intelligently merges its value with the existing attribute value on the target node. For dictionary-based attributes like `options`, it performs a dictionary update. For list-based attributes like `domain`, it extends the list.

Usage Example:
Given an existing field with a base `options` attribute: `<field name="supplier_id" options="{'no_open': 1, 'no_create': 1}"/>`

A developer can now extend this in an inherited view without overwriting: `<attribute name="options" merge="{'list_view_ref':'cm_product.cm_product_supplierinfo_tree_view'}"/>`

The result will be a combined `options` attribute: `options="{'no_open': 1, 'no_create': 1, 'list_view_ref': 'cm_product.cm_product_supplierinfo_tree_view'}"`

Description of the issue/feature this PR addresses:

Current behavior before PR:

Desired behavior after PR is merged:




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