blockifier: remove stale allow(dead_code) (#14398)

Removes a stale `#[allow(dead_code)]` from the free function
`get_compiled_class_hash_v2` in `blockifier::state::utils`. The function is
NOT dead — only the annotation is removed; no behavior changes.

Why it's stale:
- The function is `pub` and lives in a fully public module path
  (`pub mod state` in lib.rs -> `pub mod utils` in state.rs), so it is part
  of blockifier's public API. The `dead_code` lint never fires on items
  reachable from the crate root via public visibility, so the annotation
  suppresses nothing.
- It is, in fact, actively used: `blockifier_reexecution` imports it as
  `default_get_compiled_class_hash_v2` and calls it from both
  `rpc_state_reader.rs` and `offline_state_reader.rs`
  (`StateReader::get_compiled_class_hash_v2` default-impl plumbing), and
  `starknet_transaction_prover` calls it from `running/classes_provider.rs`.

Verification (RUSTC_WRAPPER unset, CARGO_INCREMENTAL=0):
- `scripts/rust_fmt.sh` — clean
- `cargo build -p blockifier` — zero dead_code/unused warnings (default cfg)
- `cargo clippy -p blockifier --all-targets` — clean; this compiles the
  lib, test and bench targets, so it also confirms the `--tests` cfg builds
  with zero dead_code warnings.

This is a pure lint-attribute removal (no codegen/runtime effect), so the
two clean builds above are the load-bearing proof.

Environmental note: `cargo check -p blockifier --features cairo_native`
could not run in this sandbox — the `tblgen v0.5.2` build dependency (an
LLVM/MLIR TableGen binding pulled in by `cairo_native`) fails its build
script because the full LLVM-19 tooling is unavailable here. This failure
happens before blockifier is compiled, is unrelated to removing a lint
attribute, and reproduces identically on `main`. The cairo_native-gated
match arm is unaffected by this change.

Co-authored-by: Claude <noreply@anthropic.com>

Author: asaf-sw

crates/blockifier/src/state/utils.rs

@@ -9,7 +9,6 @@ use crate::state::state_api::{StateReader, StateResult};
 /// Returns the compiled class hash (v2) of the given class hash.
 /// Returns `StateError::MissingCompiledClassHashV2` if no v1_class is found for the given class
 /// hash.
-#[allow(dead_code)]
 pub fn get_compiled_class_hash_v2(
     state_reader: &impl StateReader,
     class_hash: ClassHash,