Integrate the new S3 checksum types in the gateway, including `SHA512`, `MD5`, `XXHASH64`, `XXHASH3`, and `XXHASH128`. This adds checksum calculation, validation, schema handling, and test coverage for the expanded checksum support.
These external packages have been used:
- `github.com/zeebo/xxh3` for `XXHASH3` and `XXHASH128`
- `github.com/cespare/xxhash/v2` for `XXHASH64`
Adjust integration tests because `aws-sdk-go-v2/service/s3` does not support automatic checksum calculation for the new checksum algorithms and returns an SDK-level error when only the checksum algorithm is provided. Only precalculated checksum values are acceptable for these checksum types.
References:
- `https://github.com/aws/aws-sdk-go-v2/issues/3404`
- `https://github.com/aws/aws-sdk-go-v2/issues/3403`
All the integration tests used to be in a single file, which had become large, messy, and difficult to maintain. These changes split `tests.go` into multiple files, organized by logical test groups.
