[19.0][MIG] base_import_async: migration to 19.0

[YoussefEgla]

This PR ports base_import_async to 19.0.

The queue repository already contains queue_job ported on the 19.0 branch, while base_import_async is still present as an unported placeholder with installable = False.

This migration activates the addon and aligns its async import flow with the current Odoo 19 import internals.

What changed

• Bumped the addon version to 19.0.1.0.0.
• Set installable = True.
• Updated the async execute_import() path to mirror Odoo 19 preprocessing before queueing:
  • ensure_one()
  • _parse_datetime_data()
  • _handle_multi_mapping()
  • _handle_fallback_values()
• Preserved import execution context when chunk jobs call load():
  • tracking_disable
  • name_create_enabled_fields
  • import_set_empty_fields
  • import_skip_records
• Dropped the obsolete odoo.api.returns usage, which is no longer available in Odoo 19.
• Fixed the related attachment action so it resolves the actual ir.attachment linked to the queue.job record via res_model / res_id, instead of relying on stored job kwargs.

Test updates

The test module was rewritten to cover the migrated behavior more directly.

Added or updated coverage for:

• Normal synchronous import still working.
• Async import scheduling and execution of chunk jobs.
• Datetime prevalidation before queueing.
• Fallback values being applied in the async path.
• Related attachment action opening the linked attachment.

The tests were also adapted to the Odoo 19 import wizard expectations by creating base_import.import records with raw file bytes instead of base64-encoded content.

Validation performed

• Python syntax validation with py_compile on the migrated model and test files.
• Editor diagnostics reported no errors on the migrated addon.
• Manual functional validation was also performed on an Odoo 19 deployment: importing contacts with "Import in the background" created chunk jobs and those jobs completed successfully.

Notes for reviewers

• This PR only covers base_import_async.
• queue_job is already ported on 19.0 and is not modified here.
• The migration is intentionally narrow: no extra features were added beyond the compatibility fixes required to make the addon behave correctly on Odoo 19.