Steps to Reproduce:
1. Install Accounting module (without Point of Sale).
2. Create a customer.
3. Create a journal entry with that customer set only at line level.
4. Post the journal entry.
5. Open the customer form.

Issue:
The Due smart button is not visible on the partner form even though an outstanding balance exists for the customer.

Note: This issue does not reproduce when Point of Sale is installed, as the POS module overrides `_compute_has_moves` with its own implementation that checks the outstanding balance directly.

Root Cause:
The `_compute_has_moves` method queries only `account.move `for partner matching. When a partner is referenced only at the account.move.line level, the partner is never picked up by this query, resulting in `has_moves = False` and the Due button remaining hidden.

Fix:
Replaced the EXISTS-based implementation with a UNION-based approach as the EXISTS implementation evaluated the query per partner row, whereas UNION processes all partners in a single batch query. Additionally extended the UNION to also include account.move.line partner matching, ensuring partners referenced only at the line level, are correctly detected and has_moves is set to True.

Result:
The Due smart button is now correctly visible for all partners with an outstanding balance, regardless of whether the partner is set at the journal entry level or only at the line level.

owp = 6243562

Forward-Port-Of: odoo/enterprise#119084

In recent versions of PyPDF, modifying a `PageObject` directly from a `PdfFileReader` instance triggers a `PageObject.replace_contents` deprecation warning. As identified in the pypdf library's architecture updates (specifically PR #3638 [^1] and PR #3669 [^2]), a reader's page is intended to be read-only. Mutating it directly (e.g., using `mergePage` or `compressContentStreams`) before attaching it to a writer can break internal object references and cause `NullObject` errors.

This commit resolves the warning by inverting the order of operations to ensure we only mutate writable objects. The fix implements the following flow:
1. Add the unmodified source page directly to the `PdfFileWriter`.
2. Retrieve the newly created, writable output page.
3. Apply `mergePage` and `compressContentStreams` exclusively to the writer's copy of the page.

[^1]: https://github.com/py-pdf/pypdf/pull/3638
[^2]: https://github.com/py-pdf/pypdf/pull/3669

Forward-Port-Of: odoo/odoo#268865
Forward-Port-Of: odoo/odoo#267958

In recent versions of PyPDF, modifying a `PageObject` directly from a `PdfFileReader` instance triggers a `PageObject.replace_contents` deprecation warning. As identified in the pypdf library's architecture updates (specifically PR #3638 [^1] and PR #3669 [^2]), a reader's page is intended to be read-only. Mutating it directly (e.g., using `mergePage` or `compressContentStreams`) before attaching it to a writer can break internal object references and cause `NullObject` errors.

This commit resolves the warning by inverting the order of operations to ensure we only mutate writable objects. The fix implements the following flow:
1. Add the unmodified source page directly to the `PdfFileWriter`.
2. Retrieve the newly created, writable output page.
3. Apply `mergePage` and `compressContentStreams` exclusively to the writer's copy of the page.

[^1]: https://github.com/py-pdf/pypdf/pull/3638
[^2]: https://github.com/py-pdf/pypdf/pull/3669

Forward-Port-Of: odoo/enterprise#119694
Forward-Port-Of: odoo/enterprise#119239