Add transpose, power, and where operations with tests

[zoecarver]

Adds three operations that round out the compute op coverage.

Transpose:

• Follows the CB-input pattern (reads from CB, writes to DST)
• Swaps tile width and height via TTKernel transpose intrinsic
• Single-tile operation with straightforward 1:1 lowering

Power:

• DST-based operation (not CB-input) - reads from DST, writes to DST
• Takes integer exponent as an attribute
• Lowering emits repeated multiplication or uses TTKernel power intrinsic depending on exponent

Where:

• DST-based ternary operation for element-wise conditional selection
• All three operands (condition, true_value, false_value) come from DST
• Lowering emits TTKernel select/where intrinsic

Self-contained. Risk is limited to these new ops (adds new lowering, does not modify existing lowering patterns).