Implement thread-safe cache storage

- [x] 2. Implement thread-safe cache storage
  - Define global cache using `std::sync::OnceLock<RwLock<HashMap<CrcParamsCacheKey, [u64; 23]>>>`
  - Implement `get_cache()` function to initialize and return cache reference
  - Add necessary imports for `std::collections::HashMap`, `std::sync::{OnceLock, RwLock}`

Author: onethumb

.kiro/specs/crc-params-caching/tasks.md

@@ -7,7 +7,7 @@
   - Add module declaration to `src/lib.rs`
   - _Requirements: 1.1, 3.1, 3.2_
 
-- [ ] 2. Implement thread-safe cache storage
+- [x] 2. Implement thread-safe cache storage
   - Define global cache using `std::sync::OnceLock<RwLock<HashMap<CrcParamsCacheKey, [u64; 23]>>>`
   - Implement `get_cache()` function to initialize and return cache reference
   - Add necessary imports for `std::collections::HashMap`, `std::sync::{OnceLock, RwLock}`

src/cache.rs

@@ -1,3 +1,9 @@
+use std::collections::HashMap;
+use std::sync::{OnceLock, RwLock};
+
+/// Global cache storage for CRC parameter keys
+static CACHE: OnceLock<RwLock<HashMap<CrcParamsCacheKey, [u64; 23]>>> = OnceLock::new();
+
 /// Cache key for storing CRC parameters that affect key generation
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub(crate) struct CrcParamsCacheKey {
@@ -17,4 +23,11 @@ impl CrcParamsCacheKey {
             reflected,
         }
     }
+}
+
+/// Initialize and return reference to the global cache
+/// 
+/// Uses OnceLock to ensure thread-safe lazy initialization
+fn get_cache() -> &'static RwLock<HashMap<CrcParamsCacheKey, [u64; 23]>> {
+    CACHE.get_or_init(|| RwLock::new(HashMap::new()))
 }