Preserve timestamp casts when unit or timezone changes

[osipovartem]

Summary

• Keep timestamp CAST/TRY_CAST in comparison and IN expressions when the unit or timezone changes. Widening an i64 timestamp can overflow, narrowing loses precision, and attaching a non-UTC timezone can shift values. Removing the cast changes strict errors, NULLs, and comparison results.
• Preserve the existing unwrap fast path for unchanged timestamp types and other supported casts.

Validation

• cargo test -p datafusion-optimizer --lib --locked: 763 passed.
• cargo clippy -p datafusion-optimizer --lib --tests --locked: passed.
• Formatting and diff checks passed. Independent read-only review approved correctness, performance tradeoff, API compatibility, and tests.

Performance

• Retaining the cast costs CPU for in-range rows. A local Arrow 60 release microbenchmark (1M rows, 20 iterations, median of 7) measured direct equality at 3.46-3.53B rows/s versus cast plus equality at 1.19-1.23B rows/s (~2.9x slower kernel throughput). This is not an end-to-end SQL result; pruning and I/O can dominate. A safe fast path requires proven source-value bounds.

The same change has been prepared for Apache DataFusion upstream. Rustice currently pins a divergent older fork SHA, so its dependency update will be handled separately rather than including unrelated fork changes here.