Concrete v2.5: Multiple-Outputs and Iterative Functions, TFHE-rs Under the Hood, and New Truncate-PBS Operator

Concrete v2.5 introduces several significant updates, including support for multi-output functions, iterative use in loops, and new operators for efficient bit operations, enhancing the speed and productivity of homomorphic encryption (FHE) applications. The update integrates TFHE-rs into the compiler, marking a strategic shift to streamline and accelerate cryptographic processes. The introduction of composability allows functions to iterate over encrypted states, although with current limitations on function sets and input/output compatibility. New primitives like the least significant bit extraction and truncate operator facilitate faster bit manipulation, with future updates expected to expand these capabilities. The transition of 'concrete-cpu' to a facade for TFHE-rs, along with the new seeded key compression feature, promises improved speed and bandwidth efficiency in cryptographic operations, though server-side decompression is required. Overall, these advancements aim to enhance the performance and usability of Concrete in FHE applications, with further refinements anticipated in subsequent releases.