fix(rust): Fix 32-bit x86 (i686) build failure

The code was using `std::arch::x86_64::*` unconditionally for both
x86 and x86_64 architectures. On 32-bit x86 (i686), the correct
module is `std::arch::x86`, not `std::arch::x86_64`.

This caused a build failure on i686:
  error[E0432]: unresolved import `std::arch::x86_64`

The fix uses separate conditional imports:
- `std::arch::x86::*` for 32-bit x86
- `std::arch::x86_64::*` for 64-bit x86_64

Both modules provide the same SSE2 intrinsics used by find_next_zero().

Fixes #1937

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: cfsmp3

src/rust/src/avc/core.rs

@@ -8,7 +8,9 @@ use crate::{anchor_hdcc, current_fps, process_hdcc, store_hdcc, MPEG_CLOCK_FREQ}
 use lib_ccxr::common::AvcNalType;
 use lib_ccxr::util::log::DebugMessageFlag;
 use lib_ccxr::{debug, info};
-#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+#[cfg(target_arch = "x86")]
+use std::arch::x86::*;
+#[cfg(target_arch = "x86_64")]
 use std::arch::x86_64::*;
 use std::os::raw::c_void;
 use std::slice;