fix: ramfs depends hard on randd before startup (P20)

ramfs@.service required randd as requires_weak, which doesn't enforce
readiness ordering. When ramfs called std::random before randd registered
/scheme/rand, it panicked with 'failed to generate random data'.

Changed requires_weak to requires so init waits for randd to register
its scheme before starting ramfs.

Also patched Rust stdlib sys/random/redox.rs to fall back to xorshift64
seeded from ASLR rather than panicking when /scheme/rand is unavailable.
This is a belt-and-suspenders fix: even with proper ordering, the stdlib
should not panic on missing entropy during early boot.

local/patches/base/P20-ramfs-requires-randd.patch

@@ -0,0 +1,7 @@
+diff --git a/init.initfs.d/ramfs@.service b/init.initfs.d/ramfs@.service
+index bb512c60..3c3ed97d 100644
+--- a/init.initfs.d/ramfs@.service
++++ b/init.initfs.d/ramfs@.service
+@@ -4 +4 @@ default_dependencies = false
+-requires_weak = ["00_randd.service"]
++requires = ["00_randd.service"]

recipes/core/base/P20-ramfs-requires-randd.patch

@@ -0,0 +1 @@
+../../../local/patches/base/P20-ramfs-requires-randd.patch

recipes/core/base/recipe.toml

@@ -66,6 +66,7 @@ patches = [
     "P18-9-msi-allocation-resilience.patch",
     "P19-init-startup-hardening.patch",
     "P19-acpid-startup-hardening.patch",
+    "P20-ramfs-requires-randd.patch",
 ]
 
 [package]