fix: downgrade to edition 2021 and MSRV 1.80 for stable Rust compatibility (#32)

* fix: downgrade to edition 2021 and MSRV 1.82 for stable Rust compatibility

Edition 2024 requires Rust 1.85+ which breaks installation for users
on stable toolchains (e.g., Rust 1.84). MSRV 1.82 matches cachekit-core
dependency requirements.

Changes:
- rust/Cargo.toml: edition 2024 → 2021, rust-version 1.91 → 1.82

Fixes #30

* style: fix import ordering for edition 2021 rustfmt

Author: 27Bslash6

rust/Cargo.toml

@@ -1,10 +1,10 @@
 [package]
 name = "cachekit-rs"
 version = "0.2.2"
-edition = "2024"
+edition = "2021"
 authors = ["cachekit Contributors"]
 description = "High-performance storage engine for caching with compression and encryption"
-rust-version = "1.91"
+rust-version = "1.82"
 license = "MIT"
 repository = "https://github.com/cachekit-io/cachekit-py"
 homepage = "https://github.com/cachekit-io/cachekit-py"

rust/src/lib.rs

@@ -8,11 +8,12 @@ pub use cachekit_core::{ByteStorage, OperationMetrics, StorageEnvelope};
 
 #[cfg(feature = "encryption")]
 pub use cachekit_core::{
-    EncryptionError, ZeroKnowledgeEncryptor, derive_domain_key,
+    derive_domain_key,
     encryption::{
-        key_derivation::{TenantKeys, derive_tenant_keys, key_fingerprint},
+        key_derivation::{derive_tenant_keys, key_fingerprint, TenantKeys},
         key_rotation::KeyRotationState,
     },
+    EncryptionError, ZeroKnowledgeEncryptor,
 };
 
 // Python bindings (gated behind python feature)

rust/src/python_bindings.rs

@@ -92,11 +92,11 @@ impl PyByteStorage {
 
 #[cfg(feature = "encryption")]
 use cachekit_core::{
-    ZeroKnowledgeEncryptor,
     encryption::{
-        key_derivation::{TenantKeys, derive_domain_key, derive_tenant_keys, key_fingerprint},
+        key_derivation::{derive_domain_key, derive_tenant_keys, key_fingerprint, TenantKeys},
         key_rotation::KeyRotationState,
     },
+    ZeroKnowledgeEncryptor,
 };
 
 /// Python wrapper for ZeroKnowledgeEncryptor