[parabol123654]

Port of #878 (16.0) to 18.0.

Problem: with "Import in the background" checked, the batch size set in the import dialog ("Batch limit") is ignored: the file is always split in chunks of 100 lines. Odoo's import dialog sends the batch size as options["limit"], but base_import_async reads options["chunk_size"], which nothing sends anymore (the comment says it came from the module's import.js, which only sets use_queue now).

Fix: read the chunk size from options["limit"], as done in 16.0 by #878. The default of 100 is still used when no limit is given (e.g. from scripts).

Note: since the dialog's default batch limit is 2000, an import that keeps the default is now split in chunks of 2000 lines instead of 100, i.e. what the dialog shows.

Test: test_async_import_uses_batch_limit_as_chunk_size imports 3 partners with limit=1 and checks that the split job creates 3 chunk jobs. Without the fix it fails (1 != 3); with the fix it passes, along with the rest of the module's tests (3 tests on Odoo 18.0).