fix: validate transform parameters in metadata

[fallintoplace]

Summary

• add Transform::Validate to reuse bind-time transform checks during metadata validation
• reject invalid bucket/truncate parameters when parsing transform strings
• make partition specs and sort orders reject non-positive bucket/truncate parameters during schema-bound validation

Validation

• cmake -S . -B build-transform-params -G Ninja -DICEBERG_BUILD_BUNDLE=OFF -DICEBERG_BUILD_REST=OFF -DICEBERG_BUILD_SHARED=OFF
• ctest --test-dir build-transform-params -R schema_test --output-on-failure