feat: compile TFLite SVDF with its state

[asteinh]

• The TFLite frontend converts SVDF: its variable tensor becomes a state input and output, zero before the first run as in TFLite Micro.
• An int8 SVDF keeps its int16 state and time weights. The compiler admits int16 only on state tensors and stores int16 weights as int16.
• The plan writer lists the three constants with the new constants attribute and computes the int8 requantizations in float32, as TFLite Micro does.
• Refused by name: an SVDF without bias, which TFLite Micro's Prepare cannot handle; int8 state; activations other than Relu/Relu6 in float32; a variable tensor that is not one SVDF's state.
• Four corpus cases match TFLite Micro byte for byte over four consecutive runs, untiled and at the 256-byte budget: float32 and int8, batch 1 and 2, rank 1 and 2, Relu. TFLite's float reference kernels sum in a different order, so the float goldens are recorded from TFLite Micro.
• Contract case: float32 SVDF with a fused Relu against an ONNX Runtime reference.

Needs the runtime branch of the same name.