blockifier_reexecution: remove stale allow(dead_code) (#14399)

Removes a stale `#[allow(dead_code)]` from the `contract_class_mapping_dumper`
field of `RpcStateReader` in `state_reader/rpc_state_reader.rs`. The field is
NOT dead — only the annotation is removed; no behavior changes.

Why it's stale (the field is read in non-test library code):
- `RpcStateReader::get_contract_class_mapping_dumper` (rpc_state_reader.rs:393)
  reads it: `self.contract_class_mapping_dumper.lock().unwrap().clone()`. This
  public method is called from
  `RpcBlockReexecutor::get_serializable_data_reexecuted_block` (line 613).
- The `ReexecutionStateReader` impl for `RpcStateReader` reads/mutates it
  (lines 518-521) while collecting declared classes during reexecution.
- `RpcBlockReexecutor::new` clones it out of the base-block reader
  (line 572: `base_block_state_reader.contract_class_mapping_dumper.clone()`).

Since the field is read from ordinary library code, removing the annotation
produces zero dead_code warnings in both the default and --tests
configurations.

Verification (RUSTC_WRAPPER unset, CARGO_INCREMENTAL=0):
- `scripts/rust_fmt.sh` — clean
- `cargo build -p blockifier_reexecution` — zero dead_code/unused warnings
  (default cfg)
- `cargo clippy -p blockifier_reexecution --all-targets` — clean; compiles
  lib + test targets, confirming 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. The crate's `blockifier_reexecution`
test job exercises live GCloud/RPC network access, which is blocked in this
sandbox, so a full `cargo test` run was not performed; it is unaffected by
removing a lint attribute and runs in CI.

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

Author: asaf-sw

crates/blockifier_reexecution/src/state_reader/rpc_state_reader.rs

@@ -138,7 +138,6 @@ pub struct RpcStateReader {
     pub(crate) retry_config: RetryConfig,
 
     pub chain_info: ChainInfo,
-    #[allow(dead_code)]
     pub(crate) contract_class_mapping_dumper: Arc<Mutex<Option<StarknetContractClassMapping>>>,
 }