fix(wasm-utxo): pin crossbeam-epoch to >=0.9.20

Fixes RUSTSEC-2026-0204 — invalid pointer dereference in fmt::Pointer
impl for Atomic and Shared when the underlying pointer is invalid.

Author: Ranjna-G

packages/wasm-utxo/Cargo.lock

@@ -38,6 +38,9 @@ serde = { version = "1.0", features = ["derive"], optional = true }
 serde_json = { version = "1.0", optional = true }
 hex = { version = "0.4", optional = true }
 
+# Pinned to avoid RUSTSEC-2026-0204 (invalid pointer dereference in fmt::Pointer)
+crossbeam-epoch = ">=0.9.20"
+
 [dev-dependencies]
 base64 = "0.22.1"
 serde = { version = "1.0", features = ["derive"] }