dev(narugo): add e621 support

[narugo1992]

from cheesechaser.datapool import E621NewestDataPool

pool = E621NewestDataPool()

# download e621 #2010000-2010300, to directory /data/e621
pool.batch_download_to_directory(
    resource_ids=range(2010000, 2010300),
    dst_dir='/data/e621',
    max_workers=12,
)

[codecov[bot]]

Codecov Report

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

Project coverage is 82.55%. Comparing base (d87fa47) to head (9020fb5). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #12 +/- ## ========================================== + Coverage 81.09% 82.55% +1.46% ========================================== Files 29 30 +1 Lines 984 1055 +71 ========================================== + Hits 798 871 +73 + Misses 186 184 -2 ``` | [Flag](https://app.codecov.io/gh/deepghs/cheesechaser/pull/12/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepghs) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/deepghs/cheesechaser/pull/12/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepghs) | `82.55% <100.00%> (+1.46%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepghs#carryforward-flags-in-the-pull-request-comment) to find out more.

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