Fix pydantic per-row import

[abondar]

This is optimization to not import pydantic every time, but do it once in module

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing fix/pydantic-import (b58b729) with develop (35c19c8)}

[coveralls]

Pull Request Test Coverage Report for Build 21954043176

Details

• 8 of 11 (72.73%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.004%) to 82.527%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/fields/data.py	8	11	72.73%

Totals
Change from base Build 21945323563:	0.004%
Covered Lines:	10577
Relevant Lines:	12349

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💛 - Coveralls