refactor!: map BigInteger to new BigInt scalar

[IdoKendo]

This PR fixes #100 by implementing a new custom scalar Int64 following the strawberry documentation: https://strawberry.rocks/docs/types/scalars#int64

Description

The new Int64 custom scalar resolved issues of very large integers when using SQLAlchemy's BigInteger.

Types of Changes

• [x] Core
• [x] Bugfix
• [ ] New feature
• [ ] Enhancement/optimization
• [ ] Documentation

Issues Fixed or Closed by This PR

• 100

Checklist

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[botberry]

Thanks for adding the RELEASE.md file!

Here's a preview of the changelog:

---

This change implements a new custom scalar BigInt that is mapped to SQLAlchemy's BigInteger.

[erikwrede]

Thanks for the quick PR! I adjusted the title since this is a breaking change if we're strict. Still want to wait on a second opinion from @mattalbr but for me this is ready to merge. Since we don't have any unit tests on the scalar conversion yet, this is fine for me 😊

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