fix: handle file reader cancellation and empty nested concat

[InCerryGit]

Summary

This PR fixes two correctness edge cases found while reviewing the IPC reader and array concatenation paths.

File reader cancellation

ArrowFileReaderImplementation.ReadRecordBatchAsync(...) and
ReadNextRecordBatchAsync(...) accepted a caller cancellation token, but the
schema/footer loading step still called ReadSchemaAsync() without passing that
token.

That meant a canceled async file read could still continue through schema/footer
I/O before cancellation was observed later in the record batch path. This PR
passes the caller token into schema loading so cancellation is honored before
dictionary and record batch reads begin.

Empty nested array concatenation

ArrayDataConcatenator could drop the required child array structure when
concatenating nested list arrays whose parent arrays were all empty. Nested Arrow
arrays still need a valid zero-length child ArrayData; otherwise downstream
array construction can fail or produce structurally invalid nested arrays.

This PR preserves a zero-length child for all-empty nested/list inputs.

Null-only ListView concatenation

For ListView and LargeListView, null rows can have size == 0, and their
offset values should not contribute to the child slice range. The previous logic
used every offset when computing the child bounds, even for zero-size entries.

This PR computes list-view child bounds only from entries with size > 0, so
null-only inputs keep an empty child slice instead of deriving a range from null
rows.

Validation

• dotnet test test/Apache.Arrow.Tests/Apache.Arrow.Tests.csproj -c Release --filter "FullyQualifiedName~ArrowFileReaderTests.ReadRecordBatchAsync_HonorsPreCanceledTokenDuringSchemaRead|FullyQualifiedName~ArrowFileReaderTests.ReadNextRecordBatchAsync_HonorsPreCanceledTokenDuringSchemaRead|FullyQualifiedName~ArrowArrayConcatenatorTests.TestConcatenateAllEmpty|FullyQualifiedName~ArrowArrayConcatenatorTests.TestConcatenateNullOnly"
• dotnet build Apache.Arrow.sln -c Release

[CurtHagenlocher]

Thanks for these fixes!