fix: Update Dockerfile to handle bench files for dependency caching

The dummy build step needs to create placeholder bench files since
Cargo.toml references them. Also copies actual bench files during
the final build stage.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: sionsmith

Cargo.lock

@@ -3,7 +3,7 @@ resolver = "2"
 members = ["crates/kafka-remapper-core", "crates/kafka-remapper-cli"]
 
 [workspace.package]
-version = "0.5.2"
+version = "0.5.3"
 edition = "2021"
 rust-version = "1.75"
 license = "Apache-2.0"

Cargo.toml

@@ -15,18 +15,20 @@ COPY crates/kafka-remapper-core/Cargo.toml ./crates/kafka-remapper-core/
 COPY crates/kafka-remapper-cli/Cargo.toml ./crates/kafka-remapper-cli/
 
 # Create dummy source files to build dependencies
-RUN mkdir -p crates/kafka-remapper-core/src crates/kafka-remapper-cli/src && \
+RUN mkdir -p crates/kafka-remapper-core/src crates/kafka-remapper-cli/src crates/kafka-remapper-core/benches && \
     echo "pub fn dummy() {}" > crates/kafka-remapper-core/src/lib.rs && \
-    echo "fn main() {}" > crates/kafka-remapper-cli/src/main.rs
+    echo "fn main() {}" > crates/kafka-remapper-cli/src/main.rs && \
+    echo "fn main() {}" > crates/kafka-remapper-core/benches/partition_remapping.rs
 
 # Build dependencies
 RUN cargo build --release --package kafka-remapper-cli
 
 # Remove dummy source files
-RUN rm -rf crates/kafka-remapper-core/src crates/kafka-remapper-cli/src
+RUN rm -rf crates/kafka-remapper-core/src crates/kafka-remapper-cli/src crates/kafka-remapper-core/benches
 
 # Copy actual source code
 COPY crates/kafka-remapper-core/src ./crates/kafka-remapper-core/src
+COPY crates/kafka-remapper-core/benches ./crates/kafka-remapper-core/benches
 COPY crates/kafka-remapper-cli/src ./crates/kafka-remapper-cli/src
 
 # Touch source files to invalidate cache