✨ Add support for Decimal fields from Pydantic and SQLAlchemy

[robcxyz]

Per issue #30 - condecimal attributes aren't passed down into sqlalchemy types. This PR fixes that by mapping pydantic's condecimal arguments max_digits and decimal_places to sqlalchemy's decimal arguments precision and scale respectively.

main.py #395

    if issubclass(field.type_, Decimal):
        return Numeric(
            precision=getattr(field.type_, "max_digits", None),
            scale=getattr(field.type_, "decimal_places", None),
        )

Also adds an example with a test in the code_structure tutorial with a condecimal field with a few options.

[codecov]

Codecov Report

Merging #103 (0a83e2b) into main (14a9788) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #103      +/-   ##
==========================================
+ Coverage   97.27%   97.43%   +0.16%     
==========================================
  Files         175      177       +2     
  Lines        5842     5895      +53     
==========================================
+ Hits         5683     5744      +61     
+ Misses        159      151       -8     

Impacted Files	Coverage Δ
docs_src/advanced/decimal/tutorial001.py	100.00% <100.00%> (ø)
sqlmodel/main.py	81.73% <100.00%> (+2.39%)	⬆️
...sts/test_advanced/test_decimal/test_tutorial001.py	100.00% <100.00%> (ø)

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[github-actions]

📝 Docs preview for commit b3097dd at: https://61b7250eedfd1107eee4102a--sqlmodel.netlify.app

[github-actions]

📝 Docs preview for commit f3ee8b9 at: https://61b72675216a992d57cdf825--sqlmodel.netlify.app

[github-actions]

📝 Docs preview for commit 0a83e2b at: https://61b72e60030c1ad58c750965--sqlmodel.netlify.app

[tiangolo]

Awesome! Thanks for the contribution and the support @robcxyz! 🚀 🎉

I updated the docs and tests, this now has its own section in the advanced docs explaining a bit how decimals work: https://sqlmodel.tiangolo.com/advanced/decimal/

Before updating and merging this I also added this PR to Pydantic, which means that in the next Pydantic version we'll be able to have types annotated with Decimal directly instead of condecimal(), keeping editor support, etc. pydantic/pydantic#3507 🎉

This is now included in the (just released) SQLModel 0.0.5 🚀 🎉