Add PDL constraint function ktdf.is_precision - #145

Summary

• Add a new PDL constraint function, ktdf.is_precision, usable in device pattern rules to gate matches on the element precision of a linalg.generic op's output (fp16, fp32, or bf16).
• Register the constraint in PatternCache alongside the existing ktdf.is_reduction_kind / ktdf.is_inner_dim_reduction constraints.

Details

ktdfIsPrecision inspects the first output of a linalg.generic op, resolves its element type (unwrapping MemRefType/ShapedType as needed), and compares it against a caller-supplied expected_prec string attribute. It fails the match if:

• the matched op is not a linalg.generic,
• the second operand isn't a string attribute,
• the op has no outputs, or
• the element type isn't one of f16/f32/bf16.