feat: add comprehensive Rust implementation with feature parity

This commit completes the Rust implementation of mail2couch with full feature
parity to the Go version, including:

- Complete IMAP client with TLS support and retry logic
- Advanced email parsing with MIME multipart support using mail-parser
- Email attachment extraction and CouchDB storage
- Sync mode implementation with deleted message handling
- Enhanced error handling and retry mechanisms
- Identical command-line interface with bash completion
- Test configurations for both implementations

The Rust implementation now provides:
- Memory safety and type safety guarantees
- Modern async/await patterns with tokio/async-std
- Comprehensive error handling with anyhow/thiserror
- Structured logging and progress reporting
- Performance optimizations and retry logic

Test configurations created:
- rust/config-test-rust.json - Rust implementation test config
- go/config-test-go.json - Go implementation test config
- test-config-comparison.md - Detailed comparison documentation
- test-both-implementations.sh - Automated testing script

Both implementations can now be tested side-by-side with identical
configurations to validate feature parity and performance.

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

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

test-both-implementations.sh

@@ -0,0 +1,122 @@
+#!/bin/bash
+# Test script to run both Rust and Go implementations with their respective configs
+# This demonstrates feature parity between the implementations
+
+set -e
+
+echo "🧪 Testing both Rust and Go implementations with identical configurations"
+echo "=================================================="
+
+# Colors for output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+BLUE='\033[0;34m'
+YELLOW='\033[1;33m'
+NC='\033[0m' # No Color
+
+# Check if test environment is running
+check_test_env() {
+    echo -e "${BLUE}📡 Checking test environment...${NC}"
+    
+    if ! curl -s http://localhost:5984 >/dev/null; then
+        echo -e "${YELLOW}⚠️  Test environment not running. Starting it...${NC}"
+        cd test
+        ./start-test-env.sh
+        cd ..
+        echo -e "${GREEN}✅ Test environment started${NC}"
+    else
+        echo -e "${GREEN}✅ Test environment is running${NC}"
+    fi
+}
+
+# Build both implementations
+build_implementations() {
+    echo -e "${BLUE}🔨 Building implementations...${NC}"
+    
+    # Build Go implementation
+    echo -e "${BLUE}  Building Go implementation...${NC}"
+    cd go
+    go build -o mail2couch .
+    cd ..
+    echo -e "${GREEN}  ✅ Go implementation built${NC}"
+    
+    # Build Rust implementation
+    echo -e "${BLUE}  Building Rust implementation...${NC}"
+    cd rust
+    cargo build --release
+    cd ..
+    echo -e "${GREEN}  ✅ Rust implementation built${NC}"
+}
+
+# Run Go implementation
+run_go() {
+    echo -e "${BLUE}🦬 Running Go implementation...${NC}"
+    cd go
+    echo -e "${BLUE}  Using config: config-test-go.json${NC}"
+    ./mail2couch -c config-test-go.json
+    cd ..
+    echo -e "${GREEN}✅ Go implementation completed${NC}"
+}
+
+# Run Rust implementation
+run_rust() {
+    echo -e "${BLUE}🦀 Running Rust implementation...${NC}"
+    cd rust
+    echo -e "${BLUE}  Using config: config-test-rust.json${NC}"
+    ./target/release/mail2couch -c config-test-rust.json
+    cd ..
+    echo -e "${GREEN}✅ Rust implementation completed${NC}"
+}
+
+# Check results
+check_results() {
+    echo -e "${BLUE}🔍 Checking results...${NC}"
+    
+    echo -e "${BLUE}  Listing all databases:${NC}"
+    curl -s http://localhost:5984/_all_dbs | python3 -m json.tool
+    
+    echo -e "\n${BLUE}  Go implementation databases:${NC}"
+    for db in go_wildcard_all_folders_test go_work_pattern_test go_specific_folders_only; do
+        db_name="m2c_${db}"
+        if curl -s "http://localhost:5984/${db_name}" >/dev/null 2>&1; then
+            doc_count=$(curl -s "http://localhost:5984/${db_name}" | python3 -c "import sys, json; print(json.load(sys.stdin).get('doc_count', 0))")
+            echo -e "${GREEN}    ✅ ${db_name}: ${doc_count} documents${NC}"
+        else
+            echo -e "${RED}    ❌ ${db_name}: not found${NC}"
+        fi
+    done
+    
+    echo -e "\n${BLUE}  Rust implementation databases:${NC}"
+    for db in rust_wildcard_all_folders_test rust_work_pattern_test rust_specific_folders_only; do
+        db_name="m2c_${db}"
+        if curl -s "http://localhost:5984/${db_name}" >/dev/null 2>&1; then
+            doc_count=$(curl -s "http://localhost:5984/${db_name}" | python3 -c "import sys, json; print(json.load(sys.stdin).get('doc_count', 0))")
+            echo -e "${GREEN}    ✅ ${db_name}: ${doc_count} documents${NC}"
+        else
+            echo -e "${RED}    ❌ ${db_name}: not found${NC}"
+        fi
+    done
+}
+
+# Main execution
+main() {
+    echo -e "${YELLOW}🚀 Starting feature parity test...${NC}"
+    
+    check_test_env
+    build_implementations
+    
+    echo -e "\n${YELLOW}📊 Running implementations with identical configurations...${NC}"
+    run_go
+    echo ""
+    run_rust
+    
+    echo -e "\n${YELLOW}📈 Checking results...${NC}"
+    check_results
+    
+    echo -e "\n${GREEN}🎉 Feature parity test completed!${NC}"
+    echo -e "${BLUE}💡 Both implementations should have created similar databases with identical message counts.${NC}"
+    echo -e "${BLUE}🔗 View results at: http://localhost:5984/_utils${NC}"
+}
+
+# Execute main function
+main "$@"