Fix no_std and cross-platform build failures

- Add conditional import of get_arch_ops (only for supported architectures)
- Remove feature = "std" guard from fusion module import (fusion works in no_std)
- Add missing has_crc and has_sse42 fields to ArchCapabilities in no_std feature detection

Fixes build failures for:
- PowerPC targets (software fallback)
- Embedded ARM targets (thumbv7em, thumbv8m, etc.)
- WASM targets (wasm32-unknown-unknown, wasm32-wasip1, wasm32-wasip2)

Author: loadingalias

src/feature_detection.rs

@@ -175,8 +175,10 @@ unsafe fn detect_aarch64_features() -> ArchCapabilities {
 unsafe fn detect_aarch64_features() -> ArchCapabilities {
     ArchCapabilities {
         has_aes: cfg!(target_feature = "aes"),
+        has_crc: cfg!(target_feature = "crc"),
         has_sha3: cfg!(target_feature = "sha3"),
         has_sse41: false,
+        has_sse42: false,
         has_pclmulqdq: false,
         has_avx512vl: false,
         has_vpclmulqdq: false,
@@ -225,6 +227,7 @@ unsafe fn detect_x86_features() -> ArchCapabilities {
     let rust_version_supports_avx512 = check_rust_version_supports_avx512();
 
     let has_sse41 = cfg!(target_feature = "sse4.1");
+    let has_sse42 = cfg!(target_feature = "sse4.2");
     let has_pclmulqdq = has_sse41 && cfg!(target_feature = "pclmulqdq");
     let has_avx512vl =
         has_pclmulqdq && rust_version_supports_avx512 && cfg!(target_feature = "avx512vl");
@@ -233,8 +236,10 @@ unsafe fn detect_x86_features() -> ArchCapabilities {
 
     ArchCapabilities {
         has_aes: false,
+        has_crc: false,
         has_sha3: false,
         has_sse41,
+        has_sse42,
         has_pclmulqdq,
         has_avx512vl,
         has_vpclmulqdq,

src/lib.rs

@@ -194,7 +194,6 @@ use crate::crc32::consts::{
 };
 
 #[cfg(any(target_arch = "x86", target_arch = "x86_64", target_arch = "aarch64"))]
-#[cfg(feature = "std")]
 use crate::crc32::fusion;
 
 use crate::crc64::consts::{
@@ -207,6 +206,7 @@ use digest::DynDigest;
 #[cfg(feature = "alloc")]
 use digest::InvalidBufferSize;
 
+#[cfg(any(target_arch = "x86", target_arch = "x86_64", target_arch = "aarch64"))]
 use crate::feature_detection::get_arch_ops;
 #[cfg(feature = "std")]
 use std::fs::File;