feat: refactor extract command with its tests

[shadinaif]

Refactor for more usability and readability. And to prepare tests to deal with options to be added to extract command in future pull-requests

• Get babel processing out of run method into a separate method named babel_extract
• Refactor TestExtract to avoid calling the mocked extract command unless it's needed. Doing that by creating a decorator named perform_extract

Change log?

None, just a code refactor

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[shadinaif]

This one is ready @OmarIthawi , @brian-smith-tcril

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.27% :tada:

Comparison is base (c3a9831) 99.47% compared to head (d7baf2c) 99.74%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #135 +/- ## ========================================== + Coverage 99.47% 99.74% +0.27% ========================================== Files 10 10 Lines 381 399 +18 Branches 28 27 -1 ========================================== + Hits 379 398 +19 + Partials 2 1 -1 ``` | [Files Changed](https://app.codecov.io/gh/openedx/i18n-tools/pull/135?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx) | Coverage Δ | | |---|---|---| | [tests/test\_extract.py](https://app.codecov.io/gh/openedx/i18n-tools/pull/135?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openedx#diff-dGVzdHMvdGVzdF9leHRyYWN0LnB5) | `100.00% <100.00%> (+2.00%)` | :arrow_up: |

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