deps: bump anyhow 1.0.102 -> 1.0.103 (fixes RUSTSEC-2026-0190)

CI's cargo-deny flagged RUSTSEC-2026-0190: unsoundness in anyhow's
Error::downcast_mut() (UB via borrow-rule violation after Error::context),
reached transitively (n0-error / iroh + the image/rav1e chain). 1.0.103 is the
patched release; lockfile-only, no API change. cargo deny check now fully clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Cargo.lock

@@ -200,9 +200,9 @@ checksum = "940b3a0ca603d1eade50a4846a2afffd5ef57a9feac2c0e2ec2e14f9ead76000"
 
 [[package]]
 name = "anyhow"
-version = "1.0.102"
+version = "1.0.103"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7f202df86484c868dbad7eaa557ef785d5c66295e41b460ef922eca0723b842c"
+checksum = "2a4385e2e34eb35d6b3efe798b9eb88096925d87726c0798709bf56d9ed84af3"
 
 [[package]]
 name = "arbitrary"