v0.31.0-rc.6

Many thanks to @devcaeg, @EltonLobo07, @vladshcherbin and @ammarriq for contributing to this release.

To migrate from an older version, please see the official migration guide: https://valibot.dev/guides/migrate-to-v0.31.0/

• Change object check to be less stringent, making object schemas more compatible and flexible for different environments and use cases (issue #587, #602, #608)
• Fix _stringify util for custom and modified objects (issue #608)