Optimise OpenAlex table loading

[jdddog]

Optimised OpenAlex table loading and retention in several ways:

• Load data straight into the main table on the first run, rather than into the upsert table and then the main table.
• Make the upsert and delete tables expire after a period of 7 days (default value).

Also:

• Updated tests.
• Changed asserts to raising Exceptions, as asserts should not be used for control flow and can be turned off.

[codecov[bot]]

Codecov Report

Attention: 23 lines in your changes are missing coverage. Please review.

Comparison is base (440f10c) 94.13% compared to head (41ed0f6) 93.80%.

Files	Patch %	Lines
...ervatory_workflows/workflows/openalex_telescope.py	68.05%	11 Missing and 12 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #205 +/- ## ========================================== - Coverage 94.13% 93.80% -0.34% ========================================== Files 23 23 Lines 5648 5681 +33 Branches 783 797 +14 ========================================== + Hits 5317 5329 +12 - Misses 194 204 +10 - Partials 137 148 +11 ```

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