Flag for parallel mode

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 8.33333% with 11 lines in your changes missing coverage. Please review.

Project coverage is 63.71%. Comparing base (651320b) to head (358e78d).

Files	Patch %	Lines
pypechain/render/main.py	0.00%	7 Missing :warning:
pypechain/main.py	20.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #120 +/- ## ========================================== - Coverage 63.80% 63.71% -0.09% ========================================== Files 49 49 Lines 2550 2555 +5 ========================================== + Hits 1627 1628 +1 - Misses 923 927 +4 ``` | [Flag](https://app.codecov.io/gh/delvtech/pypechain/pull/120/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=delvtech) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/delvtech/pypechain/pull/120/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=delvtech) | `63.71% <8.33%> (-0.09%)` | :arrow_down: | 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=delvtech#carryforward-flags-in-the-pull-request-comment) to find out more.

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