[liwuhen]

Purpose

PR #1198 moved partition_key() out of table_upsert.rs but left the
BinaryRow import at module scope. Its remaining uses are inside the
test module, so non-test builds report an unused import. CI treats this
warning as an error through -D warnings.

Move the import into the test module to fix the warning.

Brief change log

• Remove BinaryRow from the module-level imports in table_upsert.rs.
• Import BinaryRow directly inside the existing #[cfg(test)] module.

Tests

Verified the fix locally in a temporary source copy:

• Before the fix, cargo clippy --offline --locked -p paimon --lib -- -D warnings
  fails with an unused BinaryRow import (exit code 101).
• After the fix, cargo clippy --offline --locked -p paimon --lib --tests -- -D warnings
  passes (exit code 0).

The following checks also passed:

• cargo fmt --all -- --check
• git diff --check

Clippy checked both the library and test targets. Runtime tests were not
executed because this change only relocates an import.

API and Format

No public API or persisted data format changes. Upsert behavior and test
logic remain unchanged.

Documentation

No documentation changes required.