chore: rename pblock-list directory to block-list

After PR #19 moved the Pinocchio implementation into a `pinocchio/` subdirectory, the `p` prefix on the outer directory became misleading — it no longer denotes a framework-specific implementation, since the framework distinction now lives at the inner subdir level (matching the rest of the repo, e.g. `transfer-cost/{pinocchio,anchor,native}/`).

Renaming to plain `block-list` also aligns with the on-chain identity: `pinocchio/program/src/lib.rs` declares the program with crate name `block_list` and devnet program id `BLoCKLSG2qMQ9YxEyrrKKAQzthvW4Lu8Eyv74axF6mf`.

Pure directory rename. No content changes.

Author: rocketiotemp