Fixes for shipment trackings and rather make use of long scheduler

Description

fix: error loading shipment trackings when opening wc order. Fixes https://github.com/dvdl16/woocommerce_fusion/issues/89
fix: fetch shipment providers
fix: change sync jobs to be run in long queue
fix: 'WooCommerceProduct' object is not subscriptable

Type of change

🟢 Bug fix (change which fixes an issue)
⚪ New feature (change which adds functionality)
⚪ Breaking change (fix or feature that would cause existing functionality to not work as expected)

Tests

[ ] Unit Tests have been updated or added, as required
[ ] UI Tests have been updated or added, as required

Checklist:

[x] My code follows Naming Guidelines (DocType, Field and Variable naming)
[x] No Form changes / My code follows the Form Design Guidelines
[x] My code follows the Coding Standards of this project
[x] My code follows the Code Security Guidelines of this project
[x] I have performed a self-review of my own code
[x] I have commented my code, particularly in hard-to-understand areas / No comments necessary
[x] I have made corresponding additions/changes to the documentation
[x] All business logic and validations are on the server-side / No business logic or validation changes
[x] No patches are necessary / Migration Patches have been added to the correct subdirectory of /patches and patches.txt have been updated

User Experience:

N/A

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 78.24%. Comparing base (b268584) to head (40cca6a).

Files	Patch %	Lines
...e/doctype/woocommerce_server/woocommerce_server.py	33.33%	2 Missing :warning:
...doctype/woocommerce_product/woocommerce_product.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## version-15 #91 +/- ## ============================================== - Coverage 78.38% 78.24% -0.15% ============================================== Files 23 23 Lines 1254 1255 +1 ============================================== - Hits 983 982 -1 - Misses 271 273 +2 ```

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dvdl16 / woocommerce_fusion