Deduplicate params struct if they share the same signature

[LouisGariepy]

Migrated from halcyonnouveau/clorinde#82, originally reported by @Folyd on 2025-04-01.

For example:

--! add_category
INSERT INTO
    product_categories (product_id, category_id)
VALUES
    (:product_id, :category_id) ON CONFLICT DO NOTHING;

--! remove_category
DELETE FROM
    product_categories
WHERE
    product_id = :product_id
    AND category_id = :category_id;

This is the generated code, they can be unified into one params struct.

#[derive(Clone, Copy, Debug)]
pub struct AddCategoryParams {
    pub product_id: i32,
    pub category_id: i32,
}
#[derive(Clone, Copy, Debug)]
pub struct RemoveCategoryParams {
    pub product_id: i32,
    pub category_id: i32,
}