refactor: multiple fixes

- Create unified Arch enum in utils.rs with methods for all naming conventions
- Replace 5 duplicate architecture mapping functions with single source of truth
- Add memory string validation for QEMU
- Add KVM capability verification via ioctl
- Fix TOCTOU race in resolv.conf writing using O_EXCL
- Extract magic numbers to named constants
- Use constants for stack size, buffer sizes, hostname entropy

src/distro.rs

@@ -144,39 +144,16 @@ fn parse_oci_ref(input: &str, arch: &str) -> Result<ImageSource> {
 
 /// Map architecture to OCI standard names
 pub fn map_oci_arch(arch: &str) -> String {
-    match arch {
-        "amd64" | "x86_64" => "amd64".to_string(),
-        "arm64" | "aarch64" => "arm64".to_string(),
-        "armhf" | "armv7" => "arm".to_string(),
-        "riscv64" => "riscv64".to_string(),
-        "ppc64el" | "ppc64le" => "ppc64le".to_string(),
-        "s390x" => "s390x".to_string(),
-        _ => arch.to_string(),
-    }
+    crate::utils::map_oci_arch(arch)
 }
 
 /// Map ecr architecture names to distro-specific names
 pub fn map_arch(distro: Distro, arch: &str) -> String {
-    match distro {
-        Distro::Ubuntu => match arch {
-            "amd64" => "amd64".to_string(),
-            "arm64" => "arm64".to_string(),
-            "armhf" => "armhf".to_string(),
-            "riscv64" => "riscv64".to_string(),
-            "ppc64el" => "ppc64el".to_string(),
-            "s390x" => "s390x".to_string(),
-            _ => arch.to_string(),
-        },
-        Distro::Alpine => match arch {
-            "amd64" => "x86_64".to_string(),
-            "arm64" => "aarch64".to_string(),
-            "armhf" => "armv7".to_string(),
-            "riscv64" => "riscv64".to_string(),
-            "ppc64el" => "ppc64le".to_string(),
-            "s390x" => "s390x".to_string(),
-            _ => arch.to_string(),
-        },
-    }
+    let distro_name = match distro {
+        Distro::Ubuntu => "ubuntu",
+        Distro::Alpine => "alpine",
+    };
+    crate::utils::map_arch_for_distro(distro_name, arch)
 }
 
 /// Resolve the download URL for a known distro (optimized path)