fix(ipc): handle duplicate projection indices in IPC reader

[pchintar]

Which issue does this PR close?

• Closes IPC reader projection does not handle duplicate projection indices correctly #9950 .

Rationale for this change

The current IPC reader does not correctly handle duplicate projection indices.

Schema::project(in arrow-schema/src/schema.rs) and RecordBatch::project(in arrow-array/src/record_batch.rs) both map each requested index directly, preserve the projection order and allow duplicate indices such as:

vec![1, 1]

However, the IPC reader currently uses:

projection.iter().position(|p| p == &idx)

which only returns the first matching entry. As a result, only one column is decoded even though the projected schema contains multiple fields, leading to schema/column count mismatches when constructing the RecordBatch.

This also affects reordered duplicate projections such as:

vec![2, 0, 2]

What changes are included in this PR?

• Updated IPC projection handling in arrow-ipc/src/reader.rs to preserve all matching projection entries
• Reused the decoded array for duplicate projection indices instead of decoding the same field multiple times
• Preserved projection order for reordered duplicate projections

Are these changes tested?

Yes.

Added test_projection_duplicate_indices, which verifies:

• duplicate projections (vec![1, 1])
• reordered duplicate projections (vec![2, 0, 2])

The test compares IPC projection results against RecordBatch::project.

The test fails before the fix and passes after it.

All existing arrow-ipc tests also pass cargo test -p arrow-ipc --lib

Are there any user-facing changes?

No.

[Jefffrey]

thanks @pchintar