Compare `Schema` and `StructType` fields irrespective of ordering

[kevinjqliu]

Fixes #674

Schema and StructType fields variable is represented by Tuple, which means that ordering matters when performing comparison.

Two Schemas with the same fields in different order should be consider the same

https://github.com/apache/iceberg-python/blob/7bd5d9e6c32bcc5b46993d6bfaeed50471e972ae/pyiceberg/schema.py#L88 https://github.com/apache/iceberg-python/blob/7bd5d9e6c32bcc5b46993d6bfaeed50471e972ae/pyiceberg/types.py#L346