feat: compile TFLite int8 LSTM

[asteinh]

• The TFLite frontend converts int8 UNIDIRECTIONAL_SEQUENCE_LSTM. The hidden state is an int8 state port read through its quantization, starting at its zero point as in TFLite Micro. The int16 cell state and the integer weights pass as stored, with their scales stated.
• The plan writer forms the gate and product multipliers, the cell scale's power of two and the clip in cell units as TFLite Micro's Prepare forms them.
• Refused by name: a cell other than symmetric int16; per-channel weights, for which TFLite Micro's LSTM reads one multiplier per projection.
• Corpus: batch-major and time-major int8 LSTMs, one with a cell clip, match TFLite Micro byte for byte over four consecutive runs, untiled and at the 256-byte budget.

Needs the runtime branch of the same name.