handle Null type in try_merge for Struct, List, LargeList, and Union

[zhuqi-lucas]

Describe the bug
Field::try_merge correctly handles DataType::Null for primitive types
and when self is Null, but fails when self is a compound type (Struct,
List, LargeList, Union) and from is Null. This causes Schema::try_merge
to error when merging schemas where one has a Null field and another has a
concrete compound type for the same field.

This is common in JSON inference where some files have null values for
fields that are structs/lists in other files.

To Reproduce

Expected behavior
Add DataType::Null arms to the Struct, List, LargeList, and Union
branches in Field::try_merge, consistent with how primitive types
already handle it.

Additional context

[sdf-jkl]

@zhuqi-lucas Seems like - closes didn't close the issue.

[alamb]

label_issue.py automatically added labels {'arrow'} from #9524