fix: normalize equivalent object unions

[sidsri14]

Summary

• normalize pure top-level anyOf object branches when they differ only in one property's type
• compare the normalized object union against an equivalent multi-type property in either direction
• keep correlated multi-property unions intact to avoid widening their accepted values

Closes #22

Verification

• cargo fmt --all -- --check
• cargo test --workspace --all-features
• cargo clippy --all-features --workspace --tests --examples -- -D clippy::all
• git diff --check