fix: make partition loading more efficient

[xushiyan]

Description

Fix the partition loading logic such that it

• does not skip relevant partitions
• makes file group loading parallelized

47

How are the changes test-covered

• [ ] N/A
• [x] Automated tests (unit and/or integration tests)
• [ ] Manual tests
  • [ ] Details are described below

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.10%. Comparing base (65d8ed4) to head (5713556). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #152 +/- ## ========================================== - Coverage 89.32% 89.10% -0.23% ========================================== Files 15 15 Lines 834 835 +1 ========================================== - Hits 745 744 -1 - Misses 89 91 +2 ```

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