Refactor: Move commonly used constants to constants.h

Extracted common ID constants (`kInitialSchemaId`, `kInitialColumnId`,
`kInvalidColumnId`, `kInvalidFieldId`, `kInitialSpecId`, `kInvalidPartitionFieldId`,
`kUnsortedOrderId`, etc.) from multiple headers (`schema.h`, `schema_field.h`,
`partition_spec.h`, `sort_order.h`) and centralized them into `src/iceberg/constants.h`
under the `iceberg` namespace as requested.

Updated usages across all files.

Also ran clang-format/pre-commit hooks to fix formatting.

Co-authored-by: wgtmac <4684607+wgtmac@users.noreply.github.com>

Author: google-labs-jules[bot]