Fix support for writing to nested field partition

[geruh]

Closes #2095

Rationale for this change

Currently, we can only partition on top-level valid field types, but this PR adds support for partitioning on primitive fields in a struct type using dot notation to determine the partitions against the nested structure.

Are these changes tested?

Yes added tests and tested a write against the problem in the above issue.

> aws s3 ls s3://myBucket/demo1/nestedPartition/data/
                           PRE timestamp_hour=2024-01-15-10/
                           PRE timestamp_hour=2024-01-15-11/
                           PRE timestamp_hour=2024-04-15-11/
                           PRE timestamp_hour=2024-05-15-10/

Are there any user-facing changes?

no but now can add data to tables that are partitioned by a source column that's in a struct

[kevinjqliu]

Generally LGTM! Good catch!

Heres the corresponding spec on partition columns

The source columns, selected by ids, must be a primitive type and cannot be contained in a map or list, but may be nested in a struct. For details on how to serialize a partition spec to JSON, see Appendix C.

maybe we should also gate on map/list.

[kevinjqliu]

this is fine since we use "." to implicitly reference nested fields

iceberg-python/pyiceberg/expressions/parser.py

Lines 100 to 102 in f475b8e

	@column.set_parse_action
	def _(result: ParseResults) -> Reference:
	return Reference(".".join(result.column))

iceberg-python/pyiceberg/table/update/schema.py

Lines 167 to 171 in f475b8e

	Because "." may be interpreted as a column path separator or may be used in field names, it
	is not allowed to add nested column by passing in a string. To add to nested structures or
	to add fields with names that contain "." use a tuple instead to indicate the path.
	If type is a nested type, its field IDs are reassigned when added to the existing schema.

[kevinjqliu]

interesting, so we first reference the struct field in the pa.Table and then navigate to it using struct_field's indices by name

[kevinjqliu]

maybe add this as a comment since it was not obvious

[kevinjqliu]

LGTM!