Prepare opening for FRI

[doutv]

https://github.com/okx/plonky2/blob/b74c2ac48bd25df0cbdee2e4b3871f63b631178d/plonky2/src/fri/oracle.rs#L515-L554

[doutv]

• Compute composition polynomial for each batch and combine them together as the final_poly
• LDE (FFT) to final_poly